Is having better textures than the resolution can show really that uncommon? Seems to be the case for a lot of games post-64/PS1 (at least, the ones that are popular enough to upres.)
It's uncommon for uh, decently thought out designed games on the software side. Like, that sounds mean but if you asked any software engineer to waste VRAM on stupidly high res textures in a game that's locked to a 240p screen they'd probably want to strangle you.
There might be weird production issues we don't know about, but really there's no reason to ever do this. You're just wasting optimization passes and VRAM for nothing. Like even the forward compatibility thing makes no sense because there's nothing keeping you from drawing them at x high resolution, compressing and downscaling them to 240x240 ( or lower) then leaving the raw textures on a server somewhere for the next thousand years.
I mean I'm not going to complain or anything because obviously it makes emulating them a nice treat, but there's no reason to actually leave them in the gold master wasting resources like that. My guess is they were way under their VRAM budget and in a rush to ship so instead of scaling down the textures and using that memory for something worthwhile they just said fuck it and shipped it.