Twitter has about $5B a year revenue. The fact they aren't profitable is mostly because of they were/are a badly run business.

(Note that they just about break even every year. That's a sign they can control costs, but the lack of revenue growth points to the fact that - as everyone who has used it will tell you - their ad platform is terrible).

Twitter never really got the level of usage as YT though. 300 million is what I remember for their userbase.

I suspect that any service that crosses some threshold of users will almost certainly monetize it profitably.