Stepping back a bit, we used to call these "programs". Why are they now "hosted"? I see this with recipe databases, fitness trackers, all sorts of things that have no reason to ever leave my laptop except when my backup job runs. What's the advantage of having the server and data on some device other than the one I'm using to interact with it?
To make it super easy to use the same "program" on your smartphone/tablet/laptop/desktop, wherever you are. And/or to simultaneously share access to it with friends/family. Yes, you can all just point a local app at a data share instead (the old way), but many apps aren't available across all these platforms to even make this possible across iOS, OSX, Linux, Android, and Windows, so this often doesn't work for a grou…
Thanks to all the spying/telemetry in most of those platforms once you use your privacy protecting app on them you lose the advantage of your data being self-hosted in the first place.