When I was at a meeting on Internet use for rural economic development in New Mexico back sometime in the early 2000s. I was talking to a gentleman from the New Mexico Public Regulation Commission and he was complaining that the New Mexico needed to get some old laws off the books before anything could really get done. He went on to use as an example of an old law that was still on the books on railroading (at that time, I don’t know if it has been repealed, by now) that stated that if a revenue car that originated from outside the state was in the state for so many hours (I seemed to remember it was more than 24 but less than 72 hours), that it would have to be taxed. Needless to say, this discourages any out of state railroads from building large yards in the state. If you look at towns at the state borders, you will find the yard is in the town just across the border (Raton/Trinidad). Anyway, this could be one of the reasons (it started the clock ticking, each time it entered the state). I agree with Nick that it most likely has to do with taxes.
Phil