It's just marketing and perception. They keep telling people it's cool and eventually people believe it.
As for Brum, honestly, go stand in St Phillips or St Paul's square, close your eyes, forget which city you're in, and then open and look around. You could be in London. You could be in a fancy European city. It's no different - in fact, in many ways Birmingham has nicer squares than London because it doesn't have those godawdul massive "cheap" hotel blocks ruining the outlook. I swear it's all just perception. Go to New Street and look up, above ground level. Oh hey, these are extremely nice buildings - who would have thought?
Whether this is something that a footballer like Asensio cares about or notices who is to say? These people are different to us, they move from place to place and country to country regularly, they have enough money to jet off wherever they want whenever they want. Does it really ever matter where their club is physically located?