The social media giants want to control content because that control is linked to generating revenue, mainly advertising revenue. It’s a one-way street; they want to benefit from you, the individual social media user, but they are not giving you residuals. So, the more people who are your social media “friends” — the greater your viewing audience. The social media giants want usage — views, to sell advertising.
Of course, you as the consumer have some benefits, especially if you are not paying for Facebook, for example. And they would argue that they are providing you with “useful” information, rather than advertising. Their argument is that “targeting” benefits you. This is sort of like, “We need to invade your privacy to help you.”
The social media companies, like various Internet enterprises, can be agnostic about content — it could be high-brow and intellectual, or low level and gossip. They are looking for the Internet equivalent of ratings. The more you go on social media, the more you are exposed, one way or another, to advertising, the rates of which are computed based on usage of social media by you and others.