Probably because they know that answering that question won't get flooded with angry responses. If the official reason of the issues of great plates, skill books, etc. Is what people are going to expect, then another wave of rage would come.

Can you for once release anything that isnt completely bugged or broken? Every arena you implemented so far still has bugs, even the normal one, 3vs3 is beyond repair due to heavy delay, and no main arena is bugging out, tsunade not healing with some teams, move 3-4 going before move 2, casting during CC.... the list goes on and on... rather just give the rewards and close the * arena, simply put say that you are lazy and that's it...at least i know where you stand at!