I would also add, just from my personal experience as someone interested in PPC - which I don't use for work or anything, I just find them cool - the G5 is probably one of my least favourite PPCs. I don't know why, maybe because it has the same design as a Mac Pro, so with that you get a machine that looks the same as the G5 but also does a lot of modern stuff really well. Whereas the G4s, like the G5, are also useless at what most people use computers for, but at least they have a proper retro look, which might explain why they often fetch more?
The problem with the G5 I think is that, you can not boot directly from OS9 and that's important for a lot of people who depend on OS9 to run their specialised OS9 printers and media systems that run on software that are no longer available on OSX and Win. When I spoke to one of the largest law firm in Canada which is still running a few G4 towers and iBooks across all their Canadian branches, they found it cheaper to just buy a bunch of overpriced G4s and stock em. When they die, they just yank out another G4 tower or laptop rather than convert the whole old database over. The messy privacy laws we have here in Canada and the money needed to be spent to convert all the printing and digital storage systems is so not cost effective and besides, they are storing people's info that would soon pass away in 10 years time; well maybe sooner now due to COVID and once their older clients gone to heaven, then they can remove these archaic machines as old as their clients. I get similar stories from all other businesses that it's cheaper to just buy an overpriced G4 than a G5 unless it's a G5 Quad, so that's why the G4 still holds its value. The local used Mac store here still stock G4 towers goes to show their need and popularity. If the G5 can run native OS9 including the Quad and also take SCSI cards like the Adaptec 2496, then their value would probably be more than the G4. Sadly, it's not the case with the G5.