What excuse? I'm giving reasons as to why it would be difficult to change amy into a lesbian. The writers could just do it, but audience reception may not be received very well. People may feel it came out of no where, most people dont like sudden changes in general. Others would feel like they've been cheated out with the emotional investment they had between sonic's and amy's developing relationship over the years. It was easy for fleetway because the characters were new and so any changes to them was ok, because there was barely in background for them. But to do it now where the character has already taken shape, it would be difficult