The answer is that not enough posts are getting upvoted on https://news.ycombinator.com/asknew (or https://news.ycombinator.com/newest) to clear the small threshold necessary to make it to /ask.
This has been happening for a while. Not sure what the solution is. Sometimes I go to /asknew myself and upvote the ones that seem good enough to make it to /ask, if not the frontpage, but that's a manual operation and I rarely have time.
I suppose we could fill in the empty slots with posts from /asknew but then not sure how we would pick them...