Birmingham - why off the touring map?

Whilst Birmingham does indeed get bands playing here, more often than not, bands do the London-Bristol-Manchester triangle (or equivalent), often driving past Birmingham to get to their next gig.

I did question someone on social when they announced their triangle tour, and, surprisingly, they answered. They said they tried, but would actually end up loosing money by playing a gig in Brum.
As England’s second city, in terms of population, why is this?