I'd like to add on a few points here: Platforms like FB/IG/Tiktok and other similar ones will take user data, run analytics over them, and also target and push targeted advertisement on individuals. Even google is tracking every persons move. Here's an article by Forbes:
https://www.forbes.com/sites/johnkoetsier/2020/03/11/google-is-tracking-you-on-86-of-the-top-50000-websites-on-the-planet/#53718cf3750f
which is scary enough!
On platforms like these, since they are open source, other developers and community members can see whats really going on, which makes them better from many angles.
Also another point: FB/Tiktok/Insta can control if they want to delete your posts! Here, no one can delete your posts :)