I'm going to guess they set a requirement of C#/.NET to help their move from Unity, which currently isn't supported for iOS and Android as of right now.
"As of Godot 4.0, exporting .NET projects is supported for desktop platforms (Linux, Windows and macOS). Other platforms will gain support in future 4.x releases."
"As of Godot 4.0, exporting .NET projects is supported for desktop platforms (Linux, Windows and macOS). Other platforms will gain support in future 4.x releases."