It's a shibboleth for the Rationalist community, that's why.

Well I thought the offhand remark about Bayesian priors was actually the real answer to his question of why we don’t accept arguments. I’m not going to accept some argument that contradicts a lot of what I previously thought was true unless it is very convincing (that can be achieved in a variety of ways). The remark about Bayes should have been front and center.