Exactly what kind of funding does it need?
I suspect you’re mistaking commercial companies pretending to be doing open source with actual community-driven open source.
I suspect you’re mistaking commercial companies pretending to be doing open source with actual community-driven open source.
I assume your time also has value. Open source software does not have to be shared free of charge, especially not when you need to invest your time and money to package and distribute the software and offer support for the project. The kind of puritan definition of open source that you're alluding to is only playing into the hands of the megacorps that are exploiting their users.
People deserve to be compensated for their work, especially when their work finds an active audience, even if they maintain an open source project.
Also, while open source definitely needs some funding, it can become badly harmed by too much of it, when code becomes developed purely for money and not for the usual ESR’s open source incentives.
As for the problem with a paid version - it's because when it happens, shortly afterwards the free version starts to rot. Monetisation might be good for the owner, but it's almost always terrible to user experience.
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.