Answer is:
Nostalgia. Pure, unadulterated, and self-indulgent.
Now, others will state all sorts of "reasons" like "it's a hobby" or "the other systems don't allow me to tinker", but behind it all is just nostalgia.
If you look at the 'distribution of innovation' model, the last phase/group is referred to as Laggards, and in the late '90s and early 2000s Amiga users would have fallen in this category, but we are way past this point. Whilst our ranks have a few detractors we are mostly in it for the nostalgia. On a daily basis we will use Windows/Linux/Mac OS X computers, and tablets and smartphones and games consoles and other useful gadgets, we have an Amiga to remind us of another time when things were simpler and we were part of the few that 'got it'. Like a weirdly functional photograph or a mosquito in amber that can still fly around.
I too am one of these, I have a fully functional OS3.9 A1200 w/040. Alas, it has more in common with a typewriter than a contemporary computing device. But that's a whole other philosophical topic.
