I think the "machine is always broken" meme is mostly confirmation bias. I can't even remember the last time I swung through McDonalds for a cone and the machine was down. It's probably been 5 years. Not that I do this very often, but still.

Obviously, if you pull up within an ~hour of closing, the supervisor may have made the call to go ahead and start the lengthy cleaning cycle, and ice cream isn't available. You'll find that many other menu items aren't available under these circumstances either. Worth the FTC investigating? I doubt it.

edit: I wasn't aware of the racket that is the ice cream machine business -- apparently franchises pay for expensive support contracts and the inner workings of the machine is a closely guarded trade secret.