I'm not sure if you have ever had a pool installed but it isn't cheap. Now budget for 2 - not 6m x 9m but Olympic size with grandstands etc etc. Now after 20 or 30 races one needs to be demolished - hole in the ground, landfill - gone !! Now lets build a velodrome - great for the town and keeps kids off the street etc etc. After a few days of racing we'll demolish it - yep, hole in the ground, landfill - gone. And all this within spitting distance of a city with some of the best existing sporting facilities all within a single tram ride from the GPO. Anybody been to the Melb Sports and Aquatic Centre? It sits on the outskirts of the GP track.
Incidentally I am not a sports freak nor am I particularly politically interested. IMO we should never have put a bid in given the financial state of the country / state.