It makes sense. Like you said, previous versions used the macOS design language at the time, and the current version does the same. The developer has chosen to no longer support older versions of macOS, they aren't required to. The old app still works, and anyone else can work on it if they want.
> you forgot about iOS, even though it's mentioned in the original comment, where you can't freely backport anything due to distribution being locked down
Yes you can. You can create an app today that is compatible with iOS 15.
> you forgot about iOS, even though it's mentioned in the original comment, where you can't freely backport anything due to distribution being locked down
Yes you can. You can create an app today that is compatible with iOS 15.