Imho road tyres have too less grip in general. Or at least they're too "slidy" at the edge of grip and slide and this feeling of the moment of losing grip is too small.. But that's just my feeling.
Maybe there's still pretty much constant number of players, but look at the load of different server types - Major part of users is on cruise and drift servers, there's barely few people which actually race... Excluding BL1@FBM