I think they get way more "engagement" from people who use it as their friend, and the end goal of subverting social media and creating the most powerful (read: profitable) influence engine on earth makes a lot of sense if you are a soulless ghoul.
Other than such scenarios, that "engagement" would be just useless and actually costing them more money than it makes
But I suspect that we're no more than one buyout away from that kind of thing.
The labs do appear to avoid paid advertising today. But actions today should not be taken as an indicator to mean that the next owner(s) won't behave completely soullessly manner in their effort to maximize profit at every possible expense.
On a long-enough timeline, it seems inevitable to me that advertising with LLM bots will become a real issue.
(I mean: I remember having an Internet experience that was basically devoid of advertising. It changed, and it will never change back.)