Those who produce the content have basically no control over how it is distributed and under what conditions.
I cannot choose licenses, file formats, security and usability standards, accessibility accommodations, or efficiency of design.
I can be limited in what topics I can write about which are not always clear or reasonable.
I cannot even have reasonable assurance of file integrity so visitors get what I have uploaded without modifications.
I have to allow them to put ads, comments, and links to anywhere everywhere.
They can remove me from their system or change their conditions at any time for any reason and may not even announce it.
They are notoriously technically unreliable in every sense of the word.
I have no control over basic technical things like copy restrictions (DRM) and whether I can offer downloads freely.
Finally, they are almost impossible to leave although they could be gone at the drop of the hat.