Thats the thing, if he calls your 3-bet, you're beaten.

If you follow the check-call line, you have NO idea where you stand. He keeps betting, you keep calling...you end up losing more. If you 3-bet the flop, you take the pot right there, or you cut your losses.

Had the turn or river bets been larger by villain, Hero can easily lose alot more money here taking the c/c line.