The GPL is not compatible with Apple's App Store restrictions, so giving away your source code is not sufficient to comply with the GPL.
"The primary problem is that Apple imposes numerous legal restrictions on use and distribution...through the iTunes Store Terms of Service, which is forbidden by section 6 of GPLv2."
There is also a significant difference between giving away free applications and giving away the source code. Both from an internal perspective (the company may want to charge for the product or related products or products on other platforms now or in the future) and an external perspective (the app may require other software for which the company does not have rights to release source code).
"Here's a free loaf of bread."
"Why don't you just give me the bread factory and the farms that supplied the ingredients?"
Maybe because some mega corp will figure out how to offer it as a service, and they'll get nothing for it. I support them defending themselves with a way to maybe make money on it. If they can't eat, they can't update the code.
So it's very conceivable that if your app is producing money for you, you don't want to open source the magic as it were - but if you're making money, you shouldn't expect a free ride.
However, if you aren't making money, and are still using the work of others, then it's good to contribute back - even if that's just by open sourcing your work for others to learn from and study. It's not required, but neither is it required for this framework to have a free tier, much less a truly free one that helps protect the future of your app.
Probably depends on the reasonable(?) license fee.