They can. They just have to compile it themselves (the code is available on GitHub) or find someone else to give them a compiled version (for example F-Droid which is linked from the readme on github).
Free software means that you are allowed to do a lot of stuff. It doesn’t mean you can expect to be handed everything on a silver platter. Correctly building and uploading mobile apps to an official app store is a lot of work (even more on iOS than on Android) and while I personally wouldn’t take money for it, I can completely understand when other developers do so to finance their work. Remember, open source developers also need to pay for food and housing.
They can. They just have to compile it themselves (the code is available on GitHub) or find someone else to give them a compiled version (for example F-Droid which is linked from the readme on github).
Free software means that you are allowed to do a lot of stuff. It doesn’t mean you can expect to be handed everything on a silver platter. Correctly building and uploading mobile apps to an official app store is a lot of work (even more on iOS than on Android) and while I personally wouldn’t take money for it, I can completely understand when other developers do so to finance their work. Remember, open source developers also need to pay for food and housing.