[bgsavings]

It's too far away and do cut is too slow.
Normal do works on the basis of getting the opponent to lift his arms, either to cover the men, or to attack. As the jodan player already got his arms up, all he needs is to bring his shinai down to cut.
Katate-tsuki you got about the same reach as the jodan player's men, with do, you'll most likely just miss
Also, the moment a jodan player attacks, his right arm will go down to the side, covering the right do.
My right elbow is one big bruise in the moment, from people trying kaeshi do.
I've seen a few people use gyaku-do, but they were very (very!) fast.

Jakob