https://www.thekitchn.com/why-we-drink-eggnog-at-christmas-226791
Journals and diaries from back then reveal that eggnog was a Christmas tradition. What is less clear is how drink and holiday met, hit it off, and stayed together. One can guess. The ingredients for eggnog are available year-round, but could you imagine drinking a cream-based brew with the viscosity of syrup and then heading out to plow a farm in summer? It makes much more sense that colonial Americans would've waited until winter, for an occasion worthy of breaking out the spirits (if scarce) — for Christmas, a time when the harvest was done and there wasn't much to do but celebrate.
Eggnog can hit at 20 percent+ ABV. The alcohol acts as a preservative. You can age eggnog for months. I picture a starving colonist shutting the door on a prairie wind in December and, his fresh food stores having dwindled, going down to the cellar for some reserved 'nog.
I picture my girlfriend and I at my kitchen counter, my first batch frothy, pie-spiced, spiked with the sharp bite of rum, and ready for slow drinking. And it's pretty good — more like a light milkshake than the gloppy stuff from the carton. Not life-changing. Not earth-shaking. Not even enough to transform me into more than a once-a-year 'nog drinker, but nice and sweet, thick and boozy, and enough to make me see a crack of the light.
Why do we drink eggnog? Maybe history. Maybe
tradition. Maybe to fire the memory or to point the mind down a pleasant vector and press launch. Maybe to get full. Maybe to get drunk. Maybe for the same reason we do anything in December. And maybe, yes — maybe even for taste.