I haven't used Windows in a few years (and never used OneDrive), so pinch of salt time, but...

I don't like the idea of M$ having direct access to all of my files and personal data

That and, there have been mishaps with OD deleting files

Also, i personally don't like software automagic, especially when i don't understand what is going on under the hood

Is OD just a folder? Where are my documents actually stored? What happens if my internet goes out? How much do i trust M$ to not bungle something or sell or leak my files?