Why is Pokebank even something that require online?

Seriously they could make something like dream radar that let you upload pokemon from Black/White give you 3000 storage place and that you could simply put in pokemon X/Y afterward.

I don't really care that my pokemon go in a cloud storage somewhere and I believe they could still make some kind of hack detection shit in the program.
This would make 0 problem for their server and we could use it anywhere without internet, and without the fee. (Not like 5$ was a lot anyway)