Why has the government not rebuild the Twin towers?
Well, they didn't want to rebuild it because it was like a monument.
You do know that it's under construction, and that 7 World Trade Center has been completed for 3 years now, right?
Did you also know that it was private property and the government had no obligation to rebuild or fund it - and didn't - until the original owner gave the lease to the future building to the Port Authority of New York and New Jersey in 2006 because he couldn't get the financial backing for it?
Having your tower blown up by terrorists doesn't mean the government can throw away the law and take your property and build a 1400 foot skyscraper on the land and start renting out space. It'd be different if it was a highway they were building, but it's not.