The reason we elect politicians rather than deciding how to deal with big, social issues like that ourselves is because it's a full time job. Most people don't have the time and have no obligation to research "free-software based & decentralized social networks". They don't know about it and don't have the time or education to even know there's alternatives. We're so cynical about politics that it's hard to even trust politics to solve any of this since it's all so backwards and corrupt but I believe, because of the sheer impact it has on society, this is a political problem and needs to be solved through actual laws.
I agree that being a politician is a full time job, but it's not the job you appear to think it is. The job of a politician is to get reelected. Any good the politician happens to do is a side effect that you can't count on happening again.
But we don't elect ideal politicians, we elect real ones. There has never been any such thing as a political system where the "ideal job" actually existed, and I don't see any prospect of such a system ever existing. So the specifications of the "ideal job" are irrelevant; we need to look at the real jobs that real politicians actually do.
If the data is valuable and worthy of protection, and you have no ability to provide that protection, then it is reasonable for protection to be required from the layer that is removing the individual's agency.
I don't see how a decentralized and free social network wouldn't have any privacy issues. As long as you are putting your information online, it's ripe for attacks. If you have a friend in your decentralized network that uses a malicious app, that app now has access to his/her friends list and thus your information. CA got a ton of data even from users who didn't take their quiz, but rather through friends of people who took the quiz.
The best social network, IMO, is the one you have IRL.
They do have legal obligations if they're going to sell political ads.
I don't use facebook, because I think a free-software based & decentralized social network would be the right way to do social networking, but if the rest of the people want to give away their info, fine by me.
If someone I know wants to give my info to fb, it's fine too, but he/she loses part of my trust.
I value the freedom to do whatever you want with the data you have more than the convenience of the government protecting whatever data I foolishly gave away to someone.