I mean, obviously it's not for if he just straight barrels into the ground but believe it or not when he lands he's not travelling a zillion miles per hour, he comes in slowly and at that kind of speed a helmet could make a difference.
Just like if an aeroplane fell out of the sky a seat belt isn't gonna do shit but if it judders around a bit on the runway it'll make a difference.
Also, if he hits a bird with his head at that speed the helmet might save him some discomfort...