i actually know something about this one
there's a few reasons that go beyond the aesthetic "appeal"...
1) they're heavy so deaden reverb well, and don't slip around like cheaper/lighter rugs might
2) they're hard wearing, so usually last for years
3) unlike other rugs they dont have a deep pile, so you dont trip up on them and are better suited to walking on while wearing shoes
4) they're good for drum kits as they help stop the kit bouncing about (as well as the aforementioned acoustic benefits)
and i suspect this is also the case:
5) they feel a bit eastern or mediterranean, so probably make folks feel like they're the beatles making sgt pepper or something