I don't think it's about retaining ownership, necessarily. With all of the services, your data remains yours. But reading the full paragraphs, it seems to me

I don't think it's about retaining ownership, necessarily. With all of the services, your data remains yours. But reading the full paragraphs, it seems to me that DropBox's TOS say they won't use the user's data for things like advertisements. Google's TOS makes it pretty clear that uploading to Google Drive gives them a license to use and publish the data any way they want, as long as it's stored in Google Drive.