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.

I don't think it's been shrunk, I think there just aren't enough high karma posts to fill the default (filtered) page. Old posts fall off due to karma decay and low quality posts get flagged or hidden by mods. I've seen it several times before (and thought to myself that it would be a good time to post).

As mentioned there's also asknew: https://news.ycombinator.com/asknew

Why not ask for higher karma before allowing posting?