Set on flop facing c/r

I admit I'm surprised you're showing a loss with a flopped set facing a c/r. When I flop a set in position and proceed to lead out, I'm begging to be raised. I've got 33k hands in my database, I have just 11 examples where my middle set or bottom set is facing a c/r at the flop and I'm showing a profit of 8bb per hand (never folded). Maybe this is 2nl, perhaps at 10nl there are less people willing to get in with top pair. At my level, as far as I'm concerned a set on the flop is the nuts, it doesn't lose often enough for me to worry about. Perhaps it's not so simple at higher levels.