In the case of my hometown, it's because of the geography. The closer to the equator, the warmer the weather year-round. A joke from home goes, "We've got four seasons: Nearly Summer, Summer, Still Summer and Christmas." That's a bit extreme, because autumn does have a lot of the hallmarks of the season that more temperate areas have. We also have a couple of months of cold and wet weather that we call "winter", but makes people who live further north laugh.