Having a spare hard drive that you occasionally sync up and drop off at a family member's house in addition to other backup strategies is indeed a decent idea.

However, I'm guessing that--if you're anything like me--you get lazy about refreshing it and, if something happens, you realize it's been a year since you did a fresh backup.

A cloud provider backup (as opposed to sync) is a good belt-and-suspenders cheap insurance backstop to local backups that you hopefully never need.

I have local Time Machine and Synology NAS but I also pay Backblaze a nominal amount. Companies were paying Iron Mountain large sums of money before there was a cloud.