Xbox One Unusable Without Day One Patch
Console launches rarely go off without a hitch, and it looks like the Xbox One will be no exception. In an interview with Engadget, Microsoft admitted that the Xbox One would be effectively useless without a patch coming on day one.
Senior Director Albert Penello, when asked what gamers could do with the new console out of the box said, "Nothing. You need the Day One update." Adding, "You're gonna need to take this update. It's not gonna be really an optional thing."
Current consoles are being manufactured with an outdated version of the operating system, and it highlights what we've known for some time now -- that even though these brand new consoles are already a couple of years behind modern PCs, this generation is being rushed to market.

It's not even proof that this was "rushed"; they had to build up inventory so there's been months to work on updates since the last OS build.
Answer: Capitalism and Shareholder pressure for Profit Maximizing.
When they compare the negative PR and profit generation from going something like this, companies tend to focus on net gain. From this perspective, sitting with hardware already assembled until their software patch completion is definitely not an option. One can argue why they can't parallel HW and SW development so that all HW can be equipped with the latest SW when they are assembled. They may, but it will require lots of planning and implementing, if possible. Simply put, profit first. These days executives are evaluated by quarterly earning calls, and they have less incentives to look any further than a few future quarterly results. Why more retailers open earlier on Thanksgiving in spite of seemingly rages from consumers? The same reason: net profit maximization.
- NSA
To reduce the amount of data that needs to be downloaded in the day one patch.