I think it’s the same reason YouTube can keep shooting itself in the foot and still thrive: it’s where all the eyeballs are concentrated now.
I agree, I’m a “Have your own blog / homepage” proponent myself…
…but I got as far as a domain and have paid (cheap) hosting for a few years…then installing Wordpress and dang is it way clunkier to set up than I ever imagined. 🙃