Facebook created the Feed and then figured out how to run ads on it in a way that didn't annoy users too much, combined with the laser targeting available thanks to detailed profiles and likes/follows.
Reddit does not have this, and despite years of trying new stuff, can't seem to create anything equivalent. The best they've come up with is selling users' creations for LLM training, and that has limited range with how many equal sources there are. Many of which are free.
People said they couldn’t make any money, but my thinking was “they have a billion eyeballs, they’ll figure it out.”
I feel the same about Reddit.