For a techy, buying a server and setting up a WP blog isn't that hard. However there are plenty of no-techies how don't want to do these things, they prefer managed WP. I've seen many top bloggers using managed WP services like Kinsta so that he doesn't have to worry about security, scaling, plugins, etc etc, and he can focus on his passion!
Even for a WP developer like me (who can setup a VM in GC or AWS and install WP in few mins), I always prefer managed WP