There are many reasons for this. Some of them are cultural, and other are legal.

Many Americans simply don't remember drying clothes on a clothes hanger outside, and aren't used to hanging them indoors as many Europeans do. And to be fair, indoor clothing hanging is time consuming in comparison to "transfer clothes from one machine to another".

But what many don't know is that it's often banned in many home owners' associations, and banned in many apartment leases, meaning that hanging your clothes outside is actually a luxury that many simply can't partake in.