I'm guessing that with other models like Sedona and
Sorento, the lower end of the lines are the volume sellers. I don't see nearly as many SX Sorentos as I do LX running around.
People buy Sedonas because they're the more affordable option and the
Sorento is kind of a tweener in the SUV market. (The biggest available for Kia loyalists)
The Telluride stacks up against its competition apples to apples. It's not so much of a niche vehicle like some of the Kia lineup. The mistake they made was trying to align their production with what they normally sell rather than what the segment sells. I'm not saying the top of the line model is always the volume leader in the 3 row class but it seems to be a higher percentage than say, midsize SUVs.
I'm betting Kia wondered if they were going to be able to draw different kinds of buyers to their brand. (They really don't seriously compete with with class leaders with any of their models.) In my opinion, had they gone with a more traditionally Kia looking interior, it wouldn't be nearly as popular.
So, that's probably the route they took and with what it takes to line up all the components needed to build a vehicle, changing gears isn't easy to do. They found out early that demand for higher trims was much greater than expected and then it turned into a scramble to accumulate the parts to build them. The other thing is that you can't really shelve parts for the other trims, you have to build the majority of what you planned to build.