Yeah but 3rd party apps will probably need to charge end-user for usage on top of what Dropbox is already charging for storage.
If Dropbox would do these services themselves, they could make them free because they make money from storage.
Not only that, Dropbox would effectively lock-in their users into Dropbox platform. Right now it is extremely easy to switch from Dropbox to competitor. Once you start depending on so-called Dropbox apps, you can't leave just as easily.
https://www.dropbox.com/developers