I think its because they know they'll make $ either way so they can care less where it is as long as the new arena is made. Of course this is just pure speculation but who really knows? Only they do. If its on Idrive, they'll get international fans to come more to games (tourists etc.), if its in downtown, it'll be easier for locals to visit games as it is a CENTRAL location for orlando residents. another benefit for it being in Idrive is the fact that tampa/lakeland area fans can also come to games as the drive would be 50min-1 hour which isn't too bad for crazy fans:)
I prefer it to be in downtown of course as it will boost the downtown redev projects.