I think Birmingham is second only to London population wise but all the cities vie to be the biggest, best, oldest, whatever even competing for second place! It is a matter of municipal pride which has gone on for centuries. Edinburgh, the Athens of the North and Capital of Scotland, Glasgow, 2nd City of the Empire, Aberdeen, the oil capital and so on. The competition was particularly fierce in the 19th Century when e.g. Glasgow built their spectacular City Chambers and various other cities bankrupted themselves attempting to outdo them.
As a country and village girl I find it hard to understand the mind set behind this drive to be 'bigger and best' but I suppose it is the same impulse of civic pride which prompts us to enter our towns and villages into 'Britain in Bloom' or even to support a local football team.