There's some truth to this, but I think this is half the story.

Clearly people do trade rationality for signaling (as evidenced by people changing their predictions when you ask them to bet), but people are also bad at it when they're trying (there are plenty of examples of people failing even when they don't get any signaling benefit).

You have to decide how much effort to put into living up to your epistemic potential, and how much into increasing that potential.

It seems that we work harder on the latter, as well as the former in some specific cases where we know that epistemic rationality is especially important.