To be fair, every time a Presidential motorcade goes through DC streets, said streets have to be blocked off, security has to be stationed, and tons of people who otherwise would use these streets would have to be detoured or end up being stuck in worse traffic than would otherwise be. I think the setup time for all this process would have been a lot longer than 20 minutes, and it isn’t like the President can just hop in the car and drive out there.
Wouldn’t Washington have devised some sort of subway network to avert this problem, before helicopters came on the scene.