It's great entertainment, but it's not the quickest way. while the rear wheel is airborne it is not driving. Also ,it's difficult to line up for hall bends which follows.
It is a fact that while your rear wheel is in the air it can not be driving but I suspect that as these are some of the top Superbike riders in the world they would not be airborne if it gave them even a few thousandths of a second advantage over their rivals. The higher speed of approach up the hill probably gains more in time than is lost by shutting off a little to prevent a jump.