There's a reason for that. As it was told to me, when the boundary between New Mexico and the Texas Panhandle was surveyed, Texas got to hire the surveyors. They "somehow" got 13 miles off, to the west, of course, from the line that they were supposed to survey. It was supposed to line up with the western border of Oklahoma. The current line was used for a while before New Mexico figured it out and took the dispute to the Supreme Court. The Court was persuaded that it would cause too much difficulty to sort out private land boundaries, county lines, and back taxes, so they let it stand. At least, that what I've been told. Now I'm going to have to look up the real story.
TL,DR: A state that wouldn't cheat for land don't want it enough.
ETA - According to the Texas Historical Association online handbook entry on borders, the western border of the Texas Panhandle is supposed to be the 103rd meridian. The surveying "error" was two miles west of the actual 103rd meridian. Congress confirmed that boundary as surveyed in a joint resolution on February 16, 1911.