I bet some people do. Nobody has "apps" and that many integrations like Dropbox. Plus, it runs on all major platforms, and integrate many services. So you don't have to pay for a bunch of services if you pay for Dropbox.
I do. Backup all my stuff using Duplicati to OneDrive, as it integrates quite well. Works best with that software IMHO. Quite cheap for 2TB, also use it for my parents PC back-up.