why we emulate ps3 or ps4 rather than ?!

"rewrite the system"
You mean rewrite the game to run on a PC rather than a Playstation? That costs money. Lots of money.
The game devs and publisher chose not to spend that money. Simple as that.

Not sure what you mean by "emulate". Technically, emulators are barely a step up from hacked games, as Sony can make a ton more money from you buying their console & the games for it than they ever could from officially licensing an emulator, so all of the emulators out there (especially the ones for PS3/4, Wii, & XBox 360/1/S) are done without their manufacturers' consent or legal approval.

So technically, anytime there is a "port" of a console game to PC, it's already been "rewritten" to work on the PC. Unfortunately, the track record for these ports is somewhat spotty in their execution. They seem to work better when the game developer creates the PC version as part of a multi-platform release (i.e. whenever they release a LEGO-based game, it's usually released on PC at the same time as the Playstation, XBox, & Wii/WiiU versions), so they're already in the mindset of, "we want the gaming experience to be the same across multiple platforms as much as possible, but we realize ahead of time that the coding will be different because of the platforms, so we will factor that into our development cycle".

It's too bad that there aren't really any games out there where they develop the PC version first, then work on porting it to a particular console.

Legal issues. Money.

Let's think about this question. You want a disc to work in any hardware? Compliant with any console, pc or mac. Ridicilously expensive and overly complicated. There are those who are console gamers. There are those that are PC gamers. Then there are hackers that have found an illegal way to marry the two. Feeding our nostalgia or need for gaming when developers shaft the PC gamer or vice versa. That audience is much smaller and inherently greedy. They don't want to pay for a console. They download movies, games and any other digital media through torrents. Think they want to spend hundreds on a console? It won't happen because they want what they get for free and it really isn't feasible or reasonable.

Copyright issues. You want to tear down that wall? M$ won't ever let that happen.

It's not illegal? Not going to happen.

Back in the day people had integrity and character. Now that we are in the digital age some people's moral compass is tossed aside, the ethics committee fired and character and integrity are words they never knew.

Short answer: legal & money issues.

Long answer:
-- developing is expensive, whether from a time perspective or a cash perspective. Some people, like game modders (who only craft code that adds on to the game experience, rather than writing a stand-alone game), do their work as a "labor of love". They may not charge for it, but because they're not getting paid for it they can't devote as much time to it as, say, their everyday job. And even for those who professionally develop games & consoles (i.e. get paid to do so), it takes a lot of time (hence why you don't see the companies releasing a brand-new console generation every 12 months or less). And then you have the cash cost: buying & maintaining the PCs & servers to write & test the code, building the consoles, powering & heating/cooling the building, paying your employees (including all the non-coding staff you need, like HR/payroll, cleaning, etc.), etc.
-- The console OS is the legal property of the manufacturer. Your purchase of the console grants you the right to use it as-is, but doesn't give you the right to "hack" the base coding for the console OS itself. Sony, Microsoft, & Nintendo aren't going to grant anyone the legal right to simply reverse-engineer their products & then sell it to essentially compete with their products, let alone allow someone to distribute said product for free. And they have the deep pockets to afford armies of lawyers to step in & prevent that from happening...assuming they don't simply get law enforcement involved.

And let's not forget the whole hardware compatibility issue. Remember, depending on the game a console game developer company may only have to worry about 1 (or maybe 2-3) possible hardware configurations when building the game (i.e. a PS4-exclusive game is only developed for the PS4 hardware, not for PS3 or XBox 360 hardware). In contrast, PCs have hundreds, if not thousands, of possible hardware configurations (Intel or AMD CPU, & which generation? AMD or nVidia GPU? GCN or TerraScale? CUDA or non-CUDA? DDR2, DDR3, or DDR4 RAM? ROM or RW drive? Blu-Ray, DVD, or CD?), some of which will sometimes cause conflicts that simply don't happen on consoles.

So you want someone to do all of the work to essentially reverse-engineer & rewrite an entire console OS, risk legal & financial issues with the company that produced the original console, just so that they can provide you a free file that you can stick on a USB so that you can pop a console disc into your PC & play the game without the console...& you want to complain because no one has done this yet...

So again...you're saying some random people (haxxors!!!) should just rewrite all the playstation games to run on a Windows OS and hardware?

Obviously, you have zero idea how hard that actually is. Even just for one game.

Well..for some games, they just have not chosen to spend the money for a full port onto a different platform.
Or, they have not paid for the licensing from the creator to do that.

A badly done port from console to PC is worse than no port at all. And there are many, many games where the conversion was done badly.
Earning a bad rep for the game.

If it was 'worth it' (in terms of actual profit) they would do so.

Define "rewrite the system".

What 'system' are you referring to?

They are not going to rewrite a PS OS to run on pc hardware. Just look at Windows, every piece of hardware needs drivers. There must be millions of combinations of hardware, how are they going to produce the drivers for enough variations to make these viable, let alone overcome any other challenges.

Yes, you idea is 'clear, and no, that's not going to happen.

It is impossible to emulate a PS3 properly, let alone the current gen consoles.

No, it won't. You are looking to erase boundaries between companies. Competition is healthy. Someone can just buy one product, look to a hacker and have 6 or 7 other virtual products. That will only remove about a trillion dollars from the market. Ok, that will be huge. Every time they(Sony, M$ and other companies) upgrade the hackers just add and remove lines of code. Simple

Improvement for who? People that want to play the games without having to pay full price (or even a "used" price) like the general public? That's a very entitled attitude TANSTAAFL: There Ain't No Such Thing As A Free Lunch.

If the games can be played without the consoles that the companies make, they'll stop making the consoles. Without the consoles, the game developers will stop developing console games. That'll put thousands of people out of jobs, leave hundreds of buildings to rot & decay around the world (& that's just the corporation buildings, doesn't include the homes that get vacated when the developers can't afford to pay their mortgages anymore), cause all sorts of tax revenue issues for local, regional, & national governments, etc.

And you think the hackers are going to then turn around, reengineer the OS code, make it freely available, & then start also handling game development out of the "sheer goodness of their hearts"? The primary reason that hackers do what they do is to throw the bird to authorities & boost their "street cred". Nothing boosts their reputation like hacking a corporation or government agency...but game coding just doesn't cut it for that.

Just be like Elsa, & let it go....

What you are asking for is impossible. End of story.