In warmer environments, they tend to be called screen doors, and are used when you want to leave the door open without bugs getting in. In areas with bad weather (ice storms and such), storm doors protect the door itself from the elements, especially if it’s an expensive wooden door.
Yeah, I think it’s an issue with the franchisees in the US. I give mine another try about once a year, and the past three times my burger patty has been below room temperature, and the produce noticeably old. The McDonald’s near me is just consistently mediocre, which is better.