I'd guess it's because the external chassis is really expensive, and it's silly. All the busses are there, inside the device, but nope, you have to drop severa

I'd guess it's because the external chassis is really expensive, and it's silly. All the busses are there, inside the device, but nope, you have to drop several hundreds of dollars (or more) on a box that squirts them over a expensive wire because marketing and design said so.