Well the issue comes from looking at what that actually entails. Any time you're working with code modification you're in a sticky place.
PS1requires all games to have at least some sort of modification but could be used without any adjustments at all.
PS2 is a different story, as every game will need a separate wrapper that will slow the game to work at all with the new language. Every game would need its own unique wrapper, which is not only a LOT of work, but also presents an issue on licence.
PS3 is as above, only much more work.
PS4 would likely require much less work, however you still would run into some sort of licence issue, but this is a none issue as PS4 games were all released digital, and near enough all of them have w valid licence still.
So, even if you allow players to just stick their disk in, you would still need to have a manually checked and better wrapper just to get the game working, and that's a lot of work coupled with potential legal issues.
Look at Xbox, and look at what they did with Bc. "To this day," they have done the best job on it all. But their BC releases were very sparse, and sometimes not what you expected, plus they never allowed you to just stick the disk in and play any game.
If you're hoping for some mass emulator that "just works" then, well... I don't know what to say. It would be the dream, but it's just that, a dream.