They must be trying to keep up with Hardee's in calories per sammich quota.
I admit, if I weren't on a diet, curiosity would probably lead me to try one. I suspect one would be enough in a lifetime, but you just never know when those odd combinations will turn out to be so much better than it's individual components.
I once tried a peanut butter, banana, bacon, onion, lettuce and tomato sammich. I was skeptical, but it was really pretty tasty.