I've actually considered writing a post titled "Drowning in Rationality Problems" to complain about how little we still know about the theory of rationality and how few LWers seem to be working actively on the subject, but I don't know if that's a good way to motivate people.

I don't think it's necessary to frame the large number of problems you identify as a case of "drowning". An alternative framing might be one about unexplored territory, something like "rationality is fertile ground for intellectual types who wish to acquire status by solving problems".

As for why more people aren't working on them, it could come down to simple herd effects, or something like that.