If they want their car marshalled they will allow you to do so. If they don't have the patience to allow the marshall to do his job, then it is only costing them time. Furthermore, If the driver is putting the marshall in any danger or is doing something stupid like revving the motor/engine as the marshall handles the car then they do so at their own peril. It would only take one time of having his car removed from the track to tune up his attitude.
In the end, he's in that spot due to his own driving or due to another driver, the marshall didn't put him there, and the marshall is his only friend on the track in that situation.