well I doubt the programmers were particularly well-paid, and I'm sure many were inexperienced - supposedly they often hired students.
the quality is extremely variable among bootleg games though, i wouldnt say there is such a thing as "bootleg quality" - for the ones that *are* low quality its usually down to them being rushed, underfunded, under-resourced, under-experienced etc, they had pressure from publishers to get them out of the door and not much opportunity to make a quality product even if they wanted to. some still managed it, though.
as for the lack of bootleg games for modern consoles - it's about 50% copy protection and 50% the increased difficulty of developing for them. even if you were able to make your game run on the hardware, you can't really have three underpaid people slap together a passable PS4 game in a month the way you could on the NES.
