I suspect it may be a mix of various factors:

1. The HN audience’s preferences have changed over time

2. There’s way more competition – the amount of great content to share and discuss has increased a lot

3. Gruber apparently does not write as much or as well as he did a decade or so ago (at least according to many Daring Fireball readers I know)

4. Yes, many readers don’t like him, but I would also say that many readers, especially younger ones, simply don’t care about him (related to point number 1)

5. Related to all above, Gruber’s influence and relevance in tech debates have probably declined