Manchester is defiantly independent and separate and also assuredly confident in their own independence (from London/the rest of the country). And confident in their own cultural equality, or supremacy over, even, London. Liverpool the same. It wouldn't enter their thinking to hear a chant at Chelsea or Arsenal and then adapt it for themselves.
I see the fellas in our singing bit - and in previous years/decades - and, bless 'em they do try, but they do not have this independent state of mind. They don't have the confidence. Or the wit/imagination.