If you're using TC it's going to be very hard to do a lap, much less a race, without blipping the limiter. If you're not, same difficulty in completing a session with out a little wheelspin.
Usually, when we are talking about leagues, the group mindset is strong. That leads to people not wanting to cheat against friends, rivals, and aquaintences. It's hard to be an idiot like that and stick around for a season. You just don't fit in.
Besides, the fun is in dicing at the very limit and staying on the track for 60 laps.