Well, there are people out there who will never accept the new nickname, so they may as well make some money on the old stuff. And if I know anything about UND, they are always in it to make money.
This isn't the first time Sioux stuff has been sold as part of the Legacy Collection. I don't remember hearing much about past sales of this apparel. Why is this such a big deal now? This was something agreed upon long before a new nickname was "selected". As far as the quantity being sold, I cant blame the Sioux Shop for wanting to actually sell a few items.