1911's and the .44mag

[TreeDoc]

My guess would be simply because it's a huge round! Not just ballistically but physically as well. It would have to be a giant gun not unlike the Desert Eagle. The Desert Eagle has its following but is by no means a "practical" handgun. I personally see it as a novelty and I doubt any typical manufacturer like S&W, Ruger, etc would want to tool up for such an item. Lots of engineering....likely little selling. I think the 44 Auto Mag built in the early '70s is proof positive that is the case. Heck, even "Dirty Harry's Sudden Impact" movie didn't bring any life to the cartridge!