There's a lot of basic functionality missing that users expect from social media. Handling of media is a huge one. 16 MB avatars and master quality video are handled gracefully by centralized platform...
i remember arguing about 50MB profile pictures literally 3 years ago after i had used 10GB of mobile data the first 5 days of january 2023. 3 years later, it's somewhat of an issue. people don't like image proxy caches or thing that is centralizing so the solution there would be to have clients not display profile pictures over a certain size and clients optimizing media before uploading like Amethyst does.