The best reason to 3b pre is because CO is raising a wider range than, say, UTG. I would guess that he's doing it with implied odds hands like 77 and JTs. You wouldn't get any value from them post-flop unless they got you crushed.

Even if he folds most of his range, you're picking up the pot. If he continues with the strong parts of his range, you might be even money.

But if you flat pre and the flop is ace high, are you really going to fold to his cbet when he's cbetting probably 100% of the time on an ace high flop (repping the ace)
If you call on an ace-high flop, are you going to call a double-barrel? A tripple-barrel?

I've been known to tripple-barrel bluff sometimes. Do you think flatting pre would be good against me? Against your regular villain it's actually even better because they'll call a 3b way wider than I do.

That said, I'm almost tempted to turn our hand into a bluff and lead the river.