Why wouldn't GDPR apply to apps? It's not a cookie banner requirement, it is a regulation for data protection because companies were (are) selling harvested personal details and saving it for eternity.

Having personal information isn't always a bad thing, it would be really annoying if I had to fill out a form with my bank every couple of years to tell them my address, which hasn't changed and is a legitimate interest. Amazon telling everyone that I bought some athletes foot cream is not.