How would they know? Well, because Google, in its omniscience, started to downrank them for faking views with bots (which they do not do): it shows bot percentage in traffic stats, and it skyrocketed relative to non-bot traffic (which is now less than 50%) as they started to fall from the front page (feeding the vicious circle). Presumably, Google does not know or care it is a bot when it serves ads, but correlates it later with the metrics it has from other sites that use GA or ads.
Or, perhaps, Google spots the same anomalies that my friend (an old school sysadmin who pays attention to logs) did, such as the increase of traffic along with never seen before popularity among iPhone users (who are so tech savvy that they apparently do not require CSS), or users from Dallas who famously love their QQBrowser. I’m not going to list all telltale signs as the crowd here is too hype on LLMs (which is our going theory so far, it is very timely), but my friend hopes Google learns them quickly.
These newcomers usually fake UA, use inconspicuous Western IPs (requests from Baidu/Tencent data center ranges do sign themselves as bots in UA), ignore robots.txt and load many pages very quickly.
I would assume bot traffic increase would apply to feeds, since they are of as much use for LLM training purposes.
My friend does not actually engage in stringent filtering like Rachel does, but I wonder how soon it becomes actually infeasible to operate a website with actual original content (which my friend co-writes) without either that or resorting to Cloudflare or the like for protection because of the domination of these creepy-crawlies.
Edit: Google already downranked them, not threatened to downrank. Also, traffic rose but did not skyrocket, but relative amount of bot traffic skyrocketed. (Presumably without downranking the traffic would actually skyrocket.)