Convenience and mobile devices happened. With Google photos and similar I can share photos from my phone within seconds from pretty much anywhere. For example while I'm still on vacation in a foreign country. It's much lower friction than uploading the photos to a server, likely creating some kind of album, generating looks work tokens in them, etc.
These are not incompatible with private servers. I can imagine a world where, on setting up your phone, you set up the location of the backup server, which can be a server that you own. On taking a picture, instead of syncing with Google/Apple photos, it syncs with the server that you have chosen. When you share a photo, it indicates that that photo should temporarily be moved from a private folder to a public folder on the backup server.
