Legend has it that Elmer Keith himself, master cartridge loader and hunter, got the ball rolling with reverse-loaded bullets when he found it difficult to find proper soft-point rounds for hunting deer, but the idea goes further back than that.
Some people have said it has to do with the .455 Webley Mk III, which along with the revolver introduced the “Manstopper” bullet in 1898. But that was an intentional design, an early hollowpoint. The common practice of reversed bullets stared in World War I.
During the Great War German soldiers found that their rifles were completely incapable of penetrating the armor of the British Mark I tank. But by pulling bullets and reloading them backwards they found that the bullets were capable of denting the armor if they struck it face-first.
The deformation could be bad enough that the reversed bullet could cause the armor to spall on the inside of the tank, sending potentially-lethal shrapnel flying around the inside of the tank, injuring and killing crews.
German soldiers also found that this technique could damage a rifle and injure the shooter in the process, so it was happily dumped when the German Army rolled out purpose-made armor-piercing bullets.