Some reasons for me personally:
- It works well enough. I rarely have issues (maybe once a year as you say?), and then it’s usually resolved by a device reboot. Once I had to turn iCloud sync on and off again. However, I’ve learned to avoid e.g. working on Git repos in iCloud Drive, which tends to upset the sync process.
- It’s cheap. I can get 200GB storage shared with family for €3.5/month. For example Dropbox doesn’t sell less than 2TB plans, which with family sharing becomes €17/month. That’s 5x more.
- It is the best alternative on iOS. I tried lots of other sync apps before I migrated to iCloud. Partly, this is because Apple has crippled the competition by not allowing them to sync in the background without battery-draining hacks, not allowing them to integrate directly with the Photos app, etc. Partly it is because the other cloud providers I tried didn’t integrate properly with e.g. the Files API.