I think it's also strongly due to the process that AI PRs are being rejected. For one, they usually have:
Little utility
Overly invasive changes
Bloviated PR text that sounds legit but it absolutely full of shit and self-justifying
Outright lies on metrics or testing
And an author that feels offended you "caught them" and degenerates into just a huge name calling event or a "no I dint" "yes you did" "OK, I did a little" "No you did a lot" "OK, fine I did a lot but its still worthwhile" "No its not your patch to make shiny materials slightly more correctly shiny (arguable) broke our entire rendering engine" (an actual godot PR)
So once you see the telltale signs of an AI PR, it becomes a burden to just see if "this time it's not crap".
It is shit more often than not and to save time and sanity of the real devs, the entire request is tossed into the trash