Modern stadiums are a huge money spinner, they have shops, bars, restaurants, entertainment like cinemas, bowling alleys.
It's basically like building an entire entertainment quarter, that's why outside private investors are putting the money in. Birmingham is a huge city with plenty of money about it, this stadium will have people in it all week long spending that money. It will have all the big concerts on too and probably other sports occasionally.
Look at spurs increase in revenue since they built their stadium, it's the biggest in London now. Birmingham will see an increase too and with that money they can build the club into premier league regulars. That success will bring more fans. There are still masses of untapped potential fans in that area despite having a few clubs.
All yous sneering have no idea about business. I wish Sunderland had investment to build our concourses out to increase revenue, our stadium is a good size but it's not a money spinner. Very dated.