I think it’s because it’s up to interpretation. If I wanted to see the follow up to a mistake by black and I saw the only response was a ‘good’ one for White, I’d be think wait is there a better answer not included?
The other issue is that, more than likely if we can conclude that blacks move was a mistake, there’s a good chance black playing any of the follow up moves in the sequence are also a mistake. Black would either tenuki or play a damage control sequence instead. So you either get a sequence of mistake, good/ideal, mistake, good/ideal etc or it’s all good or all ideal.
I mean you could say white is ideally following the punishment of the mistake, or Black is ideally following the path of the mistake.
But anyway once there’s a consistent policy it’s good.