Facebook has huge overheads because most of their engineering time is spent on all the creepy privacy violating things they develop and the infrastructure to run them.
If we start from scratch without all that it would be possible to make a profitable social network for a couple of bucks per month per user (or a tiered system, so heavy users or “influencers” would pay more while the base tier remains free).
GDPR makes it very difficult to touch user's private data for commercial purposes. that's the whole business of a SN so this is kind of precluded