A few years back at a JavaOne conference SUN was pushing java gaming and so I got to meet a lot of game programmers. One individual (wish I could remember his name - he probably a member here) was an "old timer" who talked about when he started game programming and actually worked on Commodore 64 and Amiga games. So being an Amiga nut, I spoke with him after his presentation on the Amiga. I asked why was the best machine for building great games during its heyday got so many bad ports, no hardware addon like PC did with flightsticks, etc?
Well, he told me it came down simply to the money. They where given X amount of time to code the port and could not go over no matter what unless they wanted to work for free! The management rational is that no matter how good or bad, most games at least sold Y copies so to insure profit they need to make sure their budget was no more than X.
So you took short cuts and never tried to do anything too original - that just took too much time.
He also told me the best Amiga games where always the originals and from studios who focused on Amiga/Commodore first then other systems. I said you mean like Cinemaware or Psygnosis and he was 'yes, they were companies who cared about their games on the Amiga!' It was why the Amiga version graphics where usually on the box art because they wanted PC/Apple/C64 people to really see the difference.
So I think with all things money does the talking and especially when it came to the Amiga. Also, as popular the Amiga was for us, it still was never a "mainstream" machine. I only knew one other person with an Amiga - my cousin - back in the day yet ALL of my friends has Atari/NES.