I imagine there might be some sponsorship reasons why it was removed. I never use YWN without an ad blocker or else my computer to explode, so I will never know.
By the way, to the OP, kiddush and arba kosos are not the same halachah. You can use grape juice for kiddush, but, according to Reb Moshe, not for the arba kosos. You’d have to see the teshuva to know his reason. We have a poster here, Daas Yochid, who has an encyclopedic knowledge of Iggros Moshe; he would probably know where to find it.