> good for them; is there some reason they shouldn't have?

Their point is that the ICC should only be admitting those who intend to abide by the rules that ICC exists to enforce. Since it was Palestine's admission you asked about their answer referred to Palestine leaders' intentions with regard to those rules.

That Israel also doesn't abide by those rules is not relevant to the question you asked. It would be relevant if the question was whether or not Israel should be admitted to the ICC (and Palestinian lack of abiding by those rules would be irrelevant to that question).