Technically the one hand grip is still taught even to this day in the Canadian Forces. Personally I doubt it will make it to the next generation of pistol, but you never know with old military traditions.
You also have to remember that the way people shot handguns was different than we do it today. It wasn't the quick shooting, rapid acquisition IPSC type shooting we do now, rather the thought process was more a aimed shot, at longer distances (which is also why the sights on many earlier handguns are so fine, because when your shooting 50m or more away, you need that fine sight). Shorter range shooting was meant to be more instinctive, but at those ranges your pistol was more meant to be a back up for your sword than anything else. When your shooting one handed, your also presenting a smaller target to the enemy, which in the days before body armour, could actually make a big difference. Finally, you have to remember you had things like dueling still, if you look at the Luger, the grip is similarly angled as how someone would grasp a fencing sword. Since sword fighting was taught anyways (and up to WWII in some cases, even expected to be used in combat), holding the pistol in a similar grip, would make sense.