It also contributes to the centralization of the web, placing more information under the control of large gatekeepers, and as a side effect, giving those gatekeepers even more influence.
Most people don't use social media via the web. They use it via dedicated apps. I think it's natural that people who don't want to deal with the tech side of things will outsource it to someone else. The idea that everyone will host their own tech is unrealistic.
It's not free for you of course because advertising isn't free and from their point of view what you'd be getting is free advertising so they want you to pay them to put it in front of your customers.
It is additional work, and requires additional knowledge.
It was also not available from most of the free web hosts that sites like these used before the https push. So investigating alternatives and migrating were required. In other words, still more work.
A local volunteer group that posts their event schedule to the web were compelled to take on the burden of https just to keep their site from being labeled as a potential threat. They don't have an IT department. They aren't tech people. The change multiplied the hassles of maintaining their site. To them, the it was all cost with practically no benefit.