The desire is relateively simply explained. Some people used to find HN interesting, but the modern set of things being upvoted isn't matching their interests anymore. They already ignore the content they don't like, the problem is the content they do like isn't there anymore. The assumption, I expect, is that if there was less LLM content the site would have more of the "older style" content they used to enjoy. I don't necessarily think that will happen, but that's my interpretation of the sentiment.
It's not supposed to be zero-sum — posting volume isn't limited, or at least I assume we're nowhere near what the servers can technically handle — but attention span is limited. Seeing a front page full of things you aren't interested in makes it harder to find the things you are interested in, and feels discouraging if you want to post one of those things (an unfortunate feedback loop).
