Why do people almost always call a check-raise on the turn

[roggles]

I don't have a specific HH to show here, because the situation actually occured in hold em, but I want to discuss it for omaha.

I feel that if a pot is HU on the turn and I cr by making it about 3 times more than he bet, I really really often get a call and then they will fold to a cbet on the river.

Of course they might be calling on a draw, but often I think it's some kind of stubbornness, but then why would they give up on the river?