To safeguard your privacy, you must avoid using third-party services. One solution is self-hosting. But self-hosting can’t work on a large scale.
Of course, it works for a tiny fraction of users, for the elite. For those who understand the issues, have the technical skills and the time to do the job.
There are technical considerations: in order to self-host well, in addition to the installation and maintenance of a server (which some solutions try to simplify), it is necessary to ensure the service continuity, i.e. the continuity of connectivity and power supply. It is also necessary to ensure the recovery of service in case of disaster, i.e. to set up a rigorous continuous replication policy, or at least a periodic backup. And then, because any service is prone to various attacks, it is necessary to carry out a 24/7 monitoring in order to detect intrusions and data theft as early as possible.
And then legal considerations if you share your hosting (family, friends, neighbours): because of the regulations that make the host of a service responsible for the data it stores, it is risky to let other people benefit from its hosting. Either we assume and we trust, or we must follow the example of third-party service providers, ensure the moderation of user content in order to guarantee the legality of content, if necessary censor it, which amounts to endorse the role of an expedited private judge.
But as simple and inexpensive as the task of self-hosting may become, too few users will be willing to make any effort in this direction because they do not see sufficient interest in it.