Technology follows all rules of economics. In the case of the Amiga, it would make sense in economic terms to just use UAE. No retro hardware needed.
But sentimentality prevails over economics. Some folks collect; others restore; some just want to continue to use (and update when need be) what they bought years ago and still maintain today.
I have 40 years of computer experience, 30 with Commodores, 27 years with the Amiga. Go figure.
