No driving
When you are in charge of running the free world, you can’t drive your own car, it is just not safe enough. The secret service drives you around as part of your security and makes sure that nothing gets in your way on route to a destination. It makes sense if you think about it.
Imagine seeing a President driving down the highway and waving at you, it would just seem a little bit bizarre. On private property, they are allowed to go a little crazy with whatever vehicle they want, just not on the open roads. So much for taking that new sports car out for a spin.