From what I've heard read from several sources--one of which is regularly slammed on here (no, not KingEric)--according to a clause in the contract with Hasbro/Dreamworks/Paramount, there was a limited window of time for Universal to open as many versions of Transformers as they wanted. When they saw how popular the ride was in Hollywood, a last-minute decision to fast-track the ride was made to allow for increased ride capacity (a hard-hitting E-ticket opening a year before Potter 2.0) at USF, as well as to slip it in the soon-closing window of time to build it. The ride was done, all they had to do essentially was file permits, hire construction companies, and pull the trigger. (They probably had to design the building, too.) According to one source, the time between the decision to build the ride and the beginning of construction was only 6 weeks. I honestly don't know if that's true or not, but it would sure make sense if it is.
I get to ride Transformers (and see all the other new attractions of the past 2 years) this coming Thursday night for the first time. Sadly, it'll be during HHN (instead of a day trip), but I'm looking forward to it!