“In short, there’s no halachic or hashkafic difference between giving Halloween candy to your neighbors for a Happy Halloween or giving Christmas presents to your neighbors for a Merry Christmas.”
Im not sure if you deliberately addedd the phrase “…for a Happy Halloween” but that is not our discussion. that is NOT the reason some here give candy nor is it R’ Yaakov’s reason. The candy is given mishum eiva or mipnei darkei shalom.
Aside from the big difference mentioned earlier here is another perhaps bigger one: Christmas presents dont have to given on Dec 25. The mailman doesnt get upset if a check is given on Dec 24, 23 etc. He doesnt even come by on Dec 25. So if it can be avoided it is better to avoid giving present on the actual day (see the Remah). However if kids come by for halloween candy on October 31 it isnt practical to say come by tomorrow.