Everyone bringing their wild theories without answering the damn question:

Yes, it's been shrunk. It was a full page of posts until very recently (changed this week?)

No idea why, perhaps because it was used as if HN were Reddit, and also Ask HN in their implementation has always been pretty bad, suffering from the same downranking system so if your Ask HN has a lively discussion, it gets quickly dropped from /ask, and only questions no one really found interesting enough to engage with remained up for days.