Y’all young ’uns are spoiled. I was effectively limited to 18 total rounds, on the belt, during my first year of sworn service, when it was a DA revolver, and no more than two reloads. More ammo was not prohibited, but it could not be visible, while in uniform. Back-up handguns were allowed, but had to be worn totally concealed. Upon completely the first years of sworn service, autos were OK for duty, but the number of reloads visible on the duty belt remained at two*, and, a flap had to cover the mag floorplate. (No totally open-topped mag pouches were allowed.)
Personally-owned shotguns were allowed, from the first day of sworn service, subject to the judgement of the Field Trainer.
OK, enough historic trivia. On a serious, practical note, mags of a length that protrude far from the grip frame of a pistol are also prone to snagging while moving through vegetation and similar intervening obstacles. Mag extensions, that replace mag floor plates, can be twisted or torqued enough to separate from the mag body. When my knees still allowed it, I climbed plenty of fences and walls, and, I did not treat hedgerows and thickets as fences, but barreled through them, as necessary.
*I gamed this, by wearing two separate mag pouches, at widely-spaced positions on the belt, so that no more than two spare mags were readily visible, from one angle of view. When I knew that I would stand for inspection, I could remove the extra items, as needed.