Size required for install much larger than app
Some app might use features that will be downloaded later on for example, google vision api require some space for it to able to be downloaded even if you are not installing it, but the app may need it. Apps also will caches files so this will also need somwle space. But from my development experience, the app may contains some features that require that amount of space. Even if the size of the app may be much less than the requirement size.