That just goes with a territory of having an iPhone. When you bought that device you signed on to a culture of consumption that is enforced by the developer of that device.
The developer can't force Apple to let the developer give it to you for free. Apple doesn't tolerate free very well and anything that is free on Apple is likely either a privacy nightmare or is paid for by some subscription you have with Apple.
This isn't a problem with the app It's a problem with the Apple.