Help Me Out

My new neighbors (okay, they aren't really new, but they are newer) leave their backdoor open all day. In the summer. As in, right now, as I write this, their door is open.

What the what?

I get this in the Midwest. I do. Nice summer day, gentle breeze.

But here? It's currently hovering around 108. No breeze.

The house has AC, so either they have it turned off or they have the world's most gigantic electicity bill.

Why would anyone do this?