For me: the retro operating systems are where it's at for having fun, but at the same time, being able to boot something modern to image a drive/edit partitions/copy files from the network/etc is also super helpful sometimes.

For me, i have some old (2000s/2010s) live CDs that i use for that purpose on PCs. On PowerPC Macs, they're powerful enough that having a vaguely modern browser is super useful for downloading software and drivers. And to do that you usually need a "modern" (snow leopard, 2008?) OS even if the hardware is ~2002

Also: for me the ultimate thing in retro computing is just _doing it because it can be done_. I spent weeks getting a PCMCIA 10/100 card working on DOS 6.22/WfW 3.11 just because i believed it could be done and i wanted it to happen. I built a Spotify frontend in .NET 2005 for 95/98 because, why not? I've got windows 2000 server on a Supermicro board from 2010 because, again, i believed it could be done, so I had to try lol