I am not sure iOS popularity would justify macOS as a server. What would be the use case? It's not app development; that is done just fine on the standard desktop macOS. It's not backend; that is done just fine on Linux servers, even in Swift if that's your thing.

> that was before iOS development took off

It was offered through the 2010s, iOS development had taken off by then, and the last release was in 2021.