But why can't that app be available on the App Store?but if they found an app they really wanted or needed, they could change it after seeing an explanation of it.
If it's an app that does something funky to your phone via the use of private APIs, then there's a reason it isn't on the App Store. Apple restrict the use of private APIs because either they aren't fully functional yet, or they're unsupported and might change in future, rendering existing apps inoperable. That's a terrible experience for the consumer.