2022 was when the degradation really took hold.
HN essentially became mainstream after the New Yorker profile, Reddit's degradation due to the mod blackout and API changes, and Lemmy flopping.
I've gotten my HN back to the pre-2022 consensus but it takes severe filtering, with around 200 posts being hidden a day. And it's those posts that drive the majority of discourse on the platform now.
The fact that throwaways like you are so normalized is a huge reason.
HN has also gotten divorced from tech and water-cooler conversations in much of the tech industry, and a lot of that seems to be because HN no longer has the same plurality of Bay/NYC/Seattle/Austin techies that it used to, and the userbase is way older than much of tech now (I was always younger than average on HN, but the amount of 1980s to early 2000s references shows that the platform has frozen in time demographically).
Ignore Reddit - HN has functionally become Slashdot (the fact that I even know what slashdot is highlights how the age demographics are so skewed on HN).
Edit: can't reply
> 2022 is when tech funding dried up...
Tech funding didn't dry up then. It just coencided with the time period that most vintages that originated in early 2010s were closing out and those that originated in 2016-18 were hitting their 5 year mark.
This meant a lot of dry-powder didn't get deployed until 2023-24.
> stands to reason that we ran out of hacker topics...
They are still being posted at the same rate based on my filtering. The difference is a massive deluge in non-"traditional HN" related content being posted, and the younger generation of techies and founders (those below 35) not using HN.