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.