iOS 15 is a really old version but if developers want to put in the effort to support old versions, why not let them? Sometimes it feels like Apple thinks I work for them and have the same priorities as they do (i.e. making more money for Apple).

They have every right to allow or disallow any apps in their store, but they shouldn’t be the arbiter of what runs on the entire platform. That’s why there should be different app stores with different rules and priorities available globally.

iOS 15 will be 6 years old in 2027. The oldest iPhone that supports iOS 15 is the iPhone 6s, released in 2015.

I think this is fair.

I bet it's entirely due to security reasons.