Why would Kasich not go? Makes no sense.
Trying to get into Kasich's mind is hard because he's really weird, but I suspect his reasoning is that Cruz is the only non-Trump that might do well on the 3/22 contests and he would prefer Cruz does poorly so Kasich might get more of the #NeverTrump boost in more favorable ground like Wisconsin.
So by canceling the debate, Kasich denies Cruz any opportunity of a breakout moment, increases the odds of a Trumping on 3/22, which he hopes will help him in better states.
