It's more that no-one cares about consistency across platforms because each of us only has one platform.
I will never see the Windows version of your app, because I don't run any Windows machines. I will never know if your Windows UI is consistent with your MacOS UI.
I do care if your app uses a bunch of key shortcuts or UI conventions that no other MacOS app uses. If I have to learn a whole new set of UI conventions just because your app decided not obey the standard MacOS UI conventions, that will annoy me a lot.
I will never see the Windows version of your app, because I don't run any Windows machines. I will never know if your Windows UI is consistent with your MacOS UI.
I do care if your app uses a bunch of key shortcuts or UI conventions that no other MacOS app uses. If I have to learn a whole new set of UI conventions just because your app decided not obey the standard MacOS UI conventions, that will annoy me a lot.