It's because of the artists. The Amiga was a much more affordable art-making machine, so many artists made graphics ON the Amiga FOR the Amiga. There were even some good-looking VGA games that under utilized the PC's capabilities because they were essentially converted Amiga games.

Now for the shameless plug... My game's protagonist is an Amiga fan and the Amiga has a little cameo in it: https://store.steampowered.com/app/3040110/Outsider/