For me its because i really liked a lot of the games and tools when I was growing up as a Kid. My amiga was my favourite toy and as I got a bit older my favourite tool for doing schoolwork too. Everytime I asked something new of it it did it better than anything else. Coming home from using a Schneider 286 PC with monochrome monitor to an Amiga was ace! :-D
So now that I'm grown up I still enjoy many, not all, of the same games on my Amiga just as I did then.
Nostalgia in part I guess and a desire to go back to something I enjoy after using a PC running windows the rest of the time.
Andy