My impression is that many rationalists enjoy believing that they update their beliefs, but in practice they're human and just as attached to preconceived notions as anyone else. But if you go around telling everyone that updating is your super-power, you're going to be a lot less humble about your own failures to do so.

If you want to see how human and tribal rationalists are, go criticize the movement as an outsider. Or try to write a mildly critical NYT piece about them and watch how they react.