On the adult subs, at least, menu links, sidebar links and banner ads, automod reply links, and by limiting your sub to only paying guests or your own managed models.
Plenty of subs blatantly allow certain brands to advertise while banning anyone else. Kind of amazed Reddit themselves haven’t put more effort into to stopping it since it kinda sidesteps their in house advertising.
Because said 100k'er are probably paying off someone inside reddit. Remember when Ebay sent some couple bloody pigs masks? Yeah evil people work at companies.
At scale they will. For now, someone else puts the effort into growth marketing, eyeball capture. Reddit eventually changes the rules, seizing control, thereby acquiring users for less human cost (as opposed to missed revenue opportunity).