There is indeed an opportunity here for other cloud providers - but "better" is fuzzy. The nice thing about iCloud is that once you set it up on a device, there is no need to configure it or authenticate ever again.
It "just works" (if it actually worked).
With Dropbox, either you are storing everything for all of your users (and paying for it), or you integrate into the user's Dropbox account - which would necessitate a fancy ol' login/authentication system. Far from seamless, and relies on your users subscribing to something that is popular but far from ubiquitous.
So... either pay through the nose for all your users' storage, or force them to jump through some circus hoops on their own. Neither are great.
It "just works" (if it actually worked).
With Dropbox, either you are storing everything for all of your users (and paying for it), or you integrate into the user's Dropbox account - which would necessitate a fancy ol' login/authentication system. Far from seamless, and relies on your users subscribing to something that is popular but far from ubiquitous.
So... either pay through the nose for all your users' storage, or force them to jump through some circus hoops on their own. Neither are great.