This is a political and legal problem, not a technical one. The internet already has the ability to make Facebook "decentralized". People have tried it to varyi

This is a political and legal problem, not a technical one. The internet already has the ability to make Facebook "decentralized". People have tried it to varying extents, and they've either languished outside of the walled garden or gotten crushed by Facebook's lawyers when they've tried to make runs to the inside for data (cf. Facebook v. Power Ventures). Our choice to analogize requests to a public HTTP server as trespass to physical property has deeply constrained the growth of the internet as a free platform that benefits its users. The EU has new data portability restrictions going in next year, and these may help some, but they aren't quite strong enough to resolve the issue.