that's because there are more of them and they've been around longer and longer term leases are starting to expire and the real estate market has changed. carpet/turf tracks are relatively new (or at least popular) for off road racing in the US. i remember a time not that long ago (12 to 15 years) when you said carpet/turf off road people looked at you like you had 2 heads and wondered why and didn't like the idea. carpet was for on road, and mainly oval. and at least local to me, people seemed to prefer parking lots to in door carpet tracks. 2 tracks that were local to me had in door on road tracks (one closed in 2013 and on closed in 2007) had paved tracks. people preferred that to carpet.
man have things shifted.