The alternative to ads is subscription services, which already exist. If people prefered subscription social media to ad based they would flock to those, but they don't.
-paraphrasing someone 300 years ago, probably.
Sometimes people pick things that are bad; that people choose something doesn’t make it somehow good.
Maybe that lack of long-term feature is endemic to the capitalist system/environment, because decade-long growth usually isn't allowed to sacrifice short-term growth. I couldn't imagine a private company like Valve Software making the same decisions.