My guess is the gun companies build what sells. They aren't geniuses, but they are smart enough to look at sales statistics. Why build them if no one buys them? With the vaunting of the .270 by Jack O'Connor still reverberating, with the fame and fable surrounding the .30-06, with the favorable reception of the 7 mm Magnum, with the great power of the .300 magnums . . . just how much sales omph do you suppose is left for the .280? What kind of guy buys a .280 as their first gun? What kind of guy buys a .280 when they already own a .30-06? What kind of guy buys a .280 when they already own a .270? When you get right down to it, it is probably the guy who owns two .30-06s, a .270, and maybe a .300 mag who just feels he has to have another middling powerful centerfire rifle and also has the necessary funds who buys the .280 . . . and that is probably a pretty thin demographic. This demographic means few sales.

Notwithstanding, I'm told the .280 is a fine cartridge. My son has said he would like to have a .280, just to have something different from most people.