Cooling system: AC but no screen door?

This house has a huge stack effect, with hot air rising with a vengeance. Today, it's hot upstairs and cool downstairs. My question, when these houses were built new, why was a screen door not part of the standard design. I'm getting ready to sell the house and haven't gotten around to adding a screen door, but think this is an obvious easy Colorado cooling measure. Why, in a 1990's McStain house, is a screen door not seen as a necessity? The house has AC, but no screen door. Go figure!