Well, here's one of those sites, they seem like a pretty legitimate resource and I know many people rely on their models for pro work:

https://kitbash3d.com [kitbash3d.com]


But that's beside the point, my main question is….what causes those UV maps to extend far beyond the 0-1 UV tile boundaries?

Well, it is of course “allowed” to have any value for UV-coordinates. I do remember that many years ago - before UDIM - wrapping of textures sometimes was “baked” into non-normalized UV coordinates.
What I meant above is that today, UVs should be “standardized”, i.e. normalized. If I pay money for data, I expect the data to be “nicely, friendly, usably”

The SF-thing you sent looks like the UV coordinates are scaled and “recentered” (they might have come from some projection pipeline, from the looks of it), so correcting those is pretty straight forward.

I would definitely contact the vendor and ask for a) information on the website about UVs being non-standard and b) if possible a “cleaned” version, again, based on the fact that you paid money for it.

That is, as usual, just a narrow-minded German-grumpy perspective. Your kilometerage may vary.

Marc

it is possible the assets were textured with repeatable materials, and that UV scaling gave a good-looking result on assets
i don't know if that is any true, but a viable explanation