I think I may have found part of the reason. The spitzer bullets in the standard .307 length will not fit in the 336, therefore they needed to cut back the case. In addition, Marlin probably wanted to resurrect this type of chambering & figured it would be best to come out with their own.
Supposedly there is an article in American Rifleman that explains the new cartridge in new detail. It would be nice to have one if you knew it stick around, but the .308 winchester is stiff competition, of course one is limited to the Model 99 Savage & Browning BLR. I have the BLR and although the gun has been useful (light & good in the woods) I would desire something in stainless and better construction.
