There is one subtle benefit of being team yellow though- you will never run out of gyms to attack and will consistently get 10 coins a day (for a takedown). If you're on blue or red and your gyms are all crowded out at level 10 (without any of your mons in it) then you're out unless you shave. Instinct also has the most GPS players (whether if legit GPS playing or 'vigilante' GPS playing to balance out the team composition bias'
You also can't blame players for putting rubbish defenders in the gyms for highest level. The only time I put my 2.8k Snorlax is to piss off the attackers but it never gets the coins because of low CP and it gets shaved quickly. So what incentive do I have to put the snorlax over my 3k mons? Not any to be honest.