Either he does it on purpose... Or because he needs more training before he fights as a pro... It is like a longjumper in the olympics who keeps slipping on the run-way. IF you do that 3 times, you are done - finished. Dirrell cannot say - hey - I am the slipper - live with it! No, he needs to sort it out - or come back when he can keep his balance. Until he is properly trained he should have a point taken each time he falls to the ground - unless if he was pushed.
I think Dirrell is the anti-Froch, Loads of skill , but scared and a bit ready to take the easy way out.