My reason is simple... I'm having fun in front of my Amigas, contrar to Windohs systems I hardly ever find myself saying "what are it doing now" or "how am I suppose to do that". C64 and Amiga was the first computers i got in contact with and I still find them more userfriendly and forgiving and they also have a special place in my heart.
Most of us know the classic amigas can't do all that the PC can do today but we don't expect it to either and even when we do we know it's just a fantasy but it's ours damnit! A PC however can never give me the pleasure the Amiga and it's comunity can (and the Amiga comunity is much stronger now than it ever was since most of the nonebelivers are gone leaving a diehard core left). :-D
Another aspect that I've come across in my later years is modding and hardhacks and there the Amiga hardware is so much more forgiving and as it's been around for so long there are numerous homemade hardware to find online that is fun to tinker with yourself. :-)