If the stadium that is to be built is to be more than just a football stadium , I don't think people should focus too much on the Commonwealth games alone.
I think that the intention would be to have an arena that can hold large non football events far into the future , large concerts would be the obvious example.
Croke Park in Dublin(capacity84,000) is regularly used for huge concerts, Springsteen, U2, Ed Sheerin have all played there and Garth Brookes was booked to play to a total crowd of 250000 over a series of concerts until planning regulations got in the way.
There is huge money to be earned by the businesses in the city from concerts such as these.
Even, if Liverpool is unsuccessful in this bid for the games, it may be successful in a future bid and having good facilities already in place would surely boost such an application.