I think it's a mix of factors - the casts lent themselves to only a handful of capable teams (plus there were no real 'alpha male' teams between TAR 11 and TAR 19 aside from Jet & Cord who had their share of flaws as racers), the legs were shorter and easier, there were fewer legs involving self-driving or complex travel, and the teams themselves were more equipped to handle the TAR metagame by preparing more, studying during the race, and being efficient in racing in general.