The alternative is that which hypotheses get anecdotes is determined by mechanisms that have absolutely no correlation, or even negative correlation, with the truth.

Doesn't look implausible to me. Here's an alternative hypothesis: the existence of anecdotes is a function of which beliefs are least supported by strong data because such beliefs need anecdotes for justification.

In general, I think anecdotes are way too filtered and too biased as an information source to be considered serious evidence. In particular, there's a real danger of treating a lot of biased anecdotes as conclusive data and that danger, seems to me, outweighs the miniscule usefulness of anecdotes.