Well it could very well be a slight inefficiency as a result of tradition or inertia or whatever. I also suspect that the probability of converting for 2 goes

Well it could very well be a slight inefficiency as a result of tradition or inertia or whatever. I also suspect that the probability of converting for 2 goes down with each subsequent attempt. You can expect teams to have a few plays installed specifically for critical 2PC attempts, and you may not want to burn those plays for marginal gain early in the game.