Consider Drive as an example. You can download the entire contents of your Drive at any time. Where do you upload it to? How many services will provide a clean and easy way to import all Drive documents? Will they maintain folder hierarchy? Individual files in Drive can also be shared with zero, a few, or all users with a given URL---can your new collaborative document editing tool be set up to manage that state? Is it automatable, or something you'll have to set up by hand for 10s - 100s - 1000s of documents?
This is the kind of thing an enterprise can pay someone to sort out, but individual users really have to care about leaving a service family (that one assumes at some point in the past they were already happy with the privacy / security tradeoff) to invest the time and effort to do so without data or functionality loss.