This is the major issue, most free and open technology is not marketed as well; isn't anywhere near as user friendly and often times takes a lot more time and effort to setup. Most people don't care enough for that.
Okay, secure E2EE backups we've more or less perfected for a while. There's good F/LOSS solutions for that. And if you're willing to pay a bit, thinks like Backblaze come to mind. In other areas it's true that open-source stuff is less polished, but not backups. I mean, a few months back Apple had a regression where they were un-deleting people's photos, that's pretty nasty.
Duplicati was easy enough to convince the family. And for our home server, I set up Restic. I agree that this later one is tricky to set up properly and grandma would definitely struggle.