FedEx does contract trucking companies to haul their freight (I once worked for one of those companies). The reason it took so long though is that, in trucking, there is a lot of sitting and waiting for things to be ready, especially if you’re not dropping-and-hooking, and have to wait for your trailer to be loaded.
There is no telling whether your package was put on a plane, was shipped by a solo driver, or was shipped by a team of two drivers who never sit still very long.
You’re also not including all the time it takes to process freight, what used to be paperwork, in order for your freight to register at the new location.
In relation to the working limits Mountainbike mentioned above, this driver might have had to stop for the night because he reached his daily 10 hour limit, especially if he had already worked 7-9 hours that day before picking up the load that had your package.