Thats the reason right there, cost would be one but the publics ability to scare politicians into not doing things these days would be the biggest.
IMO its a shame we probably wont see any more opera houses, Eiffel towers or statue of libertys anywhere in the world. Just gimmicky interactive things that are hardly a "monument" (if it isn't a symbol that represents a city on the world stage its not a monument).
It comes up often that Melbourne lacks a world class monument and that the time has passed for it to even build one. I'm surprised nothing more was built with all that gold money.
It's not entirely the public's fault - opposition governments and a hostile media trash anything of value and twist the public discourse.
Melbourne has Sydney beat on national reputation these days - its image within Australia is of a lively, thriving city while the Sydney has gained itself a sad reputation of a no-fun-town for property developers and and wealthy retirees to talk about real estate investments.
But internationally, Australia's images are still of Sydney's landmarks.
If Melbourne had the Opera House and Bridge we'd be f**ked up here!