The reason the "standard" neck diameter was .262" is that the old brass needed to be cleaned up that much in order to get consistency...it had thinner necks to start with. I would venture a guess that there are still far more .262" and .263" neck chambers making it to the line than the thicker necked versions. One reason is indeed neck tension consistency, but there are other reasons too. One is that many BR shooters have a set of carbide sizing die bushings that match up with the small neck diameters already, and at around $30 a pop, don't think a new set of bushings is in the cards. However, if someone came onto the scene and set the BR world on fire with a .269" neck chamber, BR shooters would jump on board in short order. But the fact is that there's no advantage to the thicker necks, so if it ain't broke...