It's not technology, it's cost. There's not enough demand for high DPI monitors to make a decent profit off of them. That being said, if you want to spend $25K, you can get Sony's new "4k" display... or you could spend a couple hundred bucks to get a 1080p / 1440p monitor.
Its not the technology that's holding it up, its the cost to make such a monitor. Not enough people are willing to pay bucket loads of money for a super high res monitor. Until the technology becomes cheaper, you won't see many available.