I own rifles for three Ackley Improved cartridges: an AI .219 Zipper, an AI 6mm Krag, and an AI .25 Krag. All make sense, because they create a rimmed cartridge to fill a vacent niche in the list of cartridges suitable for a single shot rifle. The .25 Niedner (which was the original name for the .25-06) antedated the .257 Roberts, so that vacent niche did not exist in the rimless cartridge lineup. The only excuse for the AI .257 Roberts was that a Remington 722 .257 could be rechambered for it and still feed through the magazine.

The 722 was one of the reasons for the poor performance of the factory round, because factory ammunition had to be loaded to feed through it, which meant that the bullet was seated much too deep, reducing the powder capacity.

I personally think that the AI .257 was popularized by Model 70 Winchester collectors, who wanted to see their unaltered original .257 caliber rifles soar in value, since there are so few of them left which have not been rechambered to the AI version.