I can't speak for others, but when I wander through a Cabelas, or Sportsmen's Warehouse, or the myriad mom&pop stores in Colorado, I see hardly any .257 Roberts on the shelves. And, I've noticed because I do like the .25 cal cartridges. (I am talking before the great 2020 ammo shortage.)
Mule Deer makes an interesting observation that maybe what we are seeing is a generational shift in attitudes towards cartridges. The older cartridges are the same as they've always been, it is the users and their expectations that are changing.
I still say the bottom line is: shoot what makes you happy. And if that is the .257 Roberts, then more power to you. I, personally, just don't accept that it is one of the better all-purpose cartridges available today.
