The internet is an evolving system and the bandwidth required to get the most use out of it will increase into the future. In ways that smarter people than I can't even predict.
Perhaps with >=1MBps connections we wouldn't need so many people transiting to and from offices?
Also, this isn't a "we could spend the money elsewhere" situation. The NBN was a business plan. An investment which would turn a profit down the line.
