Why you buy eggnog year round?

It might just be preference; however, most stores stop putting out seasonal merchandise as it gets closer to the next seasonal items. That might also mean, depending on the store the product may also be on clearance due to it getting close to the "out of date" range. That can make it much lower cost and can entice people to get some while also knowing they only really get to it certain times out of the year if it isn't something they always have access to from any store.