As I understand things, 7 went up fast because the prior building destroyed on 9/11 was constructed over a large ConEd substation. The substation was destroyed and had to be rebuilt quickly. As long as that was being done a new building on top of it went up too.
5 WTC will be the former Bankers Trust site. The PA has claimed it’s selling the site for a residential/hotel tower, but so far nothing has happened.