This is a "tradition" that ended long ago for just about any holiday. The sale is usually now a week (sometimes 2) ahead of the event so that they have nothing left.

Trying to buy candy even the week before is a crap shoot, because they are already sold out of some of the food stuff and all you have left is the junk nobody wants.

There is no cheap chocolate on sale for Halloween, same goes for the old joke of waiting until the day after Valentine's Day to get the candy at half off, or buying wrapping paper after Christmas. It just isn't a thing any more because of computerized inventory systems. They estimate how much they would sell and seemingly would rather run out early than be stuck with some extra that they have to put on sale.