If you look at St. Croix's lineup of rods, they split their series down the middle as far as what's hot in the industry and the tried and true classic desin. The Triumph and Triumph X, the Mojo and the Premier, Avid and Avid X, and the Legend Elite and Legend Xtreme are all examples of this. You have to remember they are selling to a picky crowd. Just look at the comments above and you'll find some won't buy a rod without a full cork handle, while others won't buy one that isn't a split grip, some won't buy a rod because of the color, and the list goes on. They put their new technology into these new lines to keep those rods current and on the leading edge, while keeping the rods that put them there in the first place. At the same time they try to update their series as time goes by. They can't reintroduce every series every year, so they pick and choose. At the same time they need to be aware of what's going on in the industry, and the industry had become considerably more competitive at that price point in the bass world. They improved the Mojo line and kept it at the same price point making it one of the best values on the market.
Now the Premier hasn't been redesigned for a while, but it is not targeted specifically to the bass market. They aren't technique specific, and they offer many more models. If I were to guess, they're selling just fine despite the price mainly do to their mulitspecies crossover market. I would be guessing at some point in the next few years, you'll see the Premier reintroduced after a redesign, unless their numbers stay strong enough to keep it the way it is.
There are a lot going on there, and I'm sure there's other reasons as well. What it boils down to though, is they have made the Mojo Bass one of the best bang for your buck rods on the market.