But the moment you need the new localization information, you'd have just gotten off a long flight in a new country on a data plan that might not be as cost-effective as your plan in your home country.
You can still use it without waiting for a MB of the localization file to be downloaded. (Maybe that can make much more sense to, say, social media apps where you will have to download as much data to do anything.)
I believe they optimized for that usecase.