You've got to look back to the scene in the late 80's/early 90's. There wasn't any Open/Limited back then; IIRC, the only other division was Revolver. Compensators were around and the cool kids were using .38 Super with 135gr. CP Elites, but a lot of folks were still shooting .45acp (.40 was just starting to show up). At the same time, the idea of doublestack guns shooting a Major-capable caliber was just starting to go mainstream. You gotta remember, back then, people were super freaked out about pressure and "Super Face," and most shooting .38 super major were doing it with relatively heavy bullets, first with160gr RNL (Magma mold) and then with 147gr RN (lighter bullets followed). Even the rare folks shooting 9mm Major were using heavy bullets loaded out long in .38 super mags. There were no double stack guns (or at least none commonly available) that would accept a .45acp/.38 Super length round; all the double stacks were 9x19, and virtually no one was shooting 9 Major at 9x19 lengths. There were a couple outliers like the one guy out in Colorado running 9 Major in a CZ-75, and mad scientist/gunsmith Jim Boland had figured out how to cut a 1911 in half and reweld it up to take HK P7M13 mags, but doublestacks shooting Major were *really* rare.
Then, Para-Ordnance started making frame kits (they didn't even sell complete guns back then) and folks figured out if you built a gun with a one of their kits, you'd almost double your mag capacity in .45acp to 14+1. Shortly thereafter, Chip McCormick (which later split into Tripp/STI/SVI) and Caspian came out with their frame kits. This part is conjecture, but wanting to forestall another arms race, the BOD decided to create Open and Limited Divisions and limit magazine length to 140mm in Limited, and to 170mm in Open, the idea being that singlestacks would be able to achieve close to parity with doublestacks in Open by running 10-round singlestack mags. However, no one thought to restrict the 170mm length allowance to only singlestack mags (which I think was a *big* oversight), and shortly thereafter the "big stick" was born. Round counts ballooned, mag changes in Open were largely eliminated, and I guess most folks were happy.