As long as people are willing to pay, why not? Not that I love it personally, but they'll charge what the market will bear.
Personally, I would not have thought that many people would pay the $600+ for Premium, but I'm seeing a lot more of those Premium lanyards in the parks. I will confess that the included express is a great benefit that, if you visit the parks frequently, is pretty worth it. I've surprised myself with how much I've used and enjoyed it.