Would trust-busting do any good? The main reason no practical alternatives to Facebook exist is the network effect. The main reason that competitors to Google don't do well is that people will just use the search engine that returns the most relevant results (unless your internet connection is censored). The only practical solution is regulating ethical behavior of these incomprehensibly powerful corporations.
You could have said the same about AT&T. When they broke it up, they split it into distinct entities. There is no reason we couldn't split it back up into Instagram, WhatsApp, and its other various apps. It also has tons of individual functions and features that are only bundled together because of path dependence. The Marketplace, the news feed, the home page, and the discussion forums/groups are all potentially distinct companies. You could still even have one company in charge of managing identity and authentication and make everything interoperable between the distinct branches.
Setting things up that way would make it look more like a federated platform and would take no small amount of work, both from the private companies and the government (to establish standards). But as things are now nobody has an incentive to design an internet that works like that.