I guess this begs the question... Who the fuck cares if someone hits max rank in the first day/week/month? They don't get an achievement, there are no leader boards, and they keep saying nothing you unlock is going to give you a definite advantage.
If some kid wants to grind his ass in Grifball then let him grind.
Business wise, it keeps players from feeling they have to participate in the black market to stay competitive, and keeps players from burning through all the content and trading in your game. It also prevents rampant second accounting, which devalues Trueskill matchmaking.