I reckon one of the reasons there isn't more of this stuff out there is because the whole thing is a bit of a sticky wicket:
You can't simply (or shouldn't if it's for anything other than nonprofit personal use + enjoyment) go all Ice Cube, start jacking 4 beats and put your raps (+ name) on them. I'd think the whole Mac Miller SNAFU made that abundantly clear?
Properly crediting the producer/beatsmith - Thes in this case - is also tricky: If you don't give credit at all it's essentially stealing (intellectual property) and passing it off as your own, if you state "produced by" this implies the person who made the track had executive/creative control and helped shape the final song in some way (there's a key distinction between producer and beatmaker in that sense IMO), if you simply but "beat by" or something to that effect you're still taking someone else's work without their consent.
Obviously things are different once something is officially sanctioned and approved, but I reckon that is most likely the exception rather than the norm.
Of course people do get together + collaborate but rappers licensing preexisting beats straight from the artist/producer can't be particularly common.
As far as the quality of the "new" tracks is concerned:
I was quite excited when I first heard about the People Under Detroit release, hoping it might be a full-blown tribute (similar to say Elzhi's 'Elmatic'). Sad to say I was kinda disappointed when I found out that wasn't the case and they'd "just" used the original PUTS beats (I'm generally more interested in beats than in raps; not to say I don't appreciate good vocals) and weren't really cutting it with their lyrics, concepts or flows for me either. Just skipped through a couple of tracks on bandcamp again and you can tell the raps aren't really tailored to the beat, the MCs have trouble keeping up with the tempo and/or their breath control. (A few extra practice takes + a bit more experience/improved breathing technique might have helped with the latter. Big Pun comes to mind as far as heavy breathing/occasional wheezing not necessarily detracting from an otherwise outstanding performance on the mic.)
I can appreciate the effort for what it's worth (and paying respects to the P) but TBH I'd much rather listen to the original PUTS songs.
The French + Spanish MCs don't really do much for me because their voices and flows over that relative sparse beat don't add enough of a new, unique element from my perspective. You don't need to be able to understand raps in a foreign language to pick out cadence, flow, a characteristic voice or overall presence/charisma IMO.
That's my 2 cents anyway.