Partly you’re getting downvoted because you’re not accounting for the value of the content to the user. Even if the chance of a cloud provider cancelling an account or deleting content is 0.0001%, the value of a single photo to Microsoft will be magnitudes less than to an individual.

I imagine the other reason is because they’re not mutually exclusive: For instance, Synology makes it easy to have both an in-home NAS and cloud sync.