My friend made a video using his phone to show him playing against bots on a
poker site which I won't name...
it was a 6-max cash table and his 4 opponents would all sit out instantly when he sat out... and as soon as my friend would sit back in, the 4 opponents would immediately also sit back in and begin playing
blatantly obvious that it was both a collusion team AND a bot team on his table
I suspect sites run their own bots, for instance, advertise inflated guaranteed prize pools in tournaments which very often aren't met, which means the tournament has a significant overlay in the prize pool... well, that's easy enough for the site to remedy, just run their own army of bots in those tournaments to scrape off a portion of the prize pool, and they can meet the guarantee in secret, behind the scenes, while making it look like they are hugely generous with tournament overlays, which attracts more players to the site, increasing their rake.