Comment by dessant

From a quick look on GitHub the projects were not just an initial effort with little time invested in after release, but were actively developed for years. This year alone there are several releases which contain new features.

If I'm not mistaken, they were publishing the exact same version on both app stores, and the apps could be purchased or some of the features were put behind in-app purchases on Google Play. This is a reasonable funding model that has allowed many open source apps to thrive, though in this developer's case maybe it did not meet their needs.