It's great when you're a kid, or at least it used to be. Go around the neighborhood with your friends dressed up as something, get shit tons of candy, usually there's some kind of party at a friend or relative's house.
You get a bit older, start noticing girls, they notice you notice and start wearing costumes you really like looking at. As you get older the amount of candy diminishes but is replaced by booze until one day you're a full fledged adult (not just a person over eighteen), have shit to deal with and it's just another night.
But it's fun to watch people go through those stages you went through. Also I'm pretty sure it's a conspiracy to sell millions of dollars worth of candy that would otherwise just sit on a shelf.