Some more thoughts.
The irony in the final sentence of my last post has not eluded me.
My missus also pointed out that certain demographic groups might not think the carpets are kak at all.
There were some interesting comments in the discussion at MarginalRevolution (the original via). Some people made the point that wear and tear can't be the whole answer, because plenty of places have the same problems and don't have loud carpets.
I'm sure the answer is that it's a mix of things. Wear and tear is undoubtedly an issue and probably a big factor, but I'd speculate that the carpets are there to complement the flashing lights and sounds and general visual chaos, all of which is intended to generate a sense of excitement and sensory agitation; I'm sure it's all very psychological and stuff.
Tangentially, another commenter said that that cinema carpets are designed to hide popcorn. Now that's plausible!