Some of the social media discussed on this site:
Commercial social media sites all either operate on ads (capturing your attention, profiling your interests, showing personalised ads, i.e. selling your data to advertisers), or on venture capital (investors are paying the bills in the hopes of selling it later to the public or to a big company). Future profits are promised via ads.
Edward Vielmetti then added another point:
Facebook is openly hostile to its own users. It blocks private messages with links to content Facebook does not approve of, and the types of content that are blocked or allowed, should greatly trouble people. They practically hold our data hostage, and have put considerable roadblocks in place over the past several years to make it more difficult to access information, even for developers. In 2014, they intentionally manipulated posts to make certain users more depressed1 in an experiment that should have made everyone reconsider their interactions with the network. On the surface, many casual users may not notice how Facebook’s hands have grown tighter around their walled garden of data, but for developers and content creators, the signs are everywhere and should trouble everyone.