Black Sabbath has had a bigger influence on music than all of those Manchester bands combined I’m sorry
I sometimes ponder the materialist explanation for why Manchester has a much bigger cultural impact upon Britain, given that it is almost half the size of Birmingham in terms of population.
Just on the basis of music, Manchester has Joy Division, New Order, the Happy Mondays, the Stone Roses, Elbow, Oasis, The Fall, Buzzcocks, the Chemical Brothers, A Certain Ratio, The Verve, the list goes on.
What does Birmingham have? UB40 and Black Sabbath?
It's probably partly down to the fact that Manchester was a big student city in the post-war period, through to today.
And Manchester/the North West in general seems to have a stronger regional identity and civic pride than the Midlands, perhaps due to its relatively higher demographic concentration. I haven't come up with many other reasons beyond that.