There's an interesting parallel between Judo ne waza and defensive handgun shooting. They both underwent a period in the early- to mid-twentieth century during which aspects of their core technical skills stagnated or atrophied. Though the best intentions motivated both, their repercussions lasted through the end of the century, and offer valuable guidance about the what and how of martial instruction, and how it relates to competition.
Kanō Jigorō and early Judoka got a lot right with Judo: the focus on pressure testing, training safety, and eliding "deadly" techniques that couldn't be practiced with the former in mind. But early in the 20th century, the rules of Judo were modified to limit "boring" ground-fighting. In an era when matches were viewed directly by the audience (some close, many farther away) and not primarily by broadcast television or video recording, this makes some sense. Imagine watching a BJJ match from a hundred feet away. Compare that to a Judo match from the same distance. It's usually easier to visually "parse" what's going on when two people are standing with a little separation between them, as opposed to knotted up in a pretzel on the ground. I don't know what the popular climate was like at the time, but perhaps this was a critical rule change to "save" Judo from obscurity or disinterest in Japan. Regardless, this isn't about assigning blame.
It had another effect, though, which was to mute the practice of ne waza. And why shouldn't it? If you know you'll spend only a small fraction of your time on the ground in competition, that de-emphasis will filter down through competition-oriented instruction all the way to beginners. Less training time means less brain-power exerted to maintain efficacy, discover improvements, and efficiently teach. It's only natural. Because this rule change was ignored in other places where Judo had spread (e.g., Brazil, Russia) those folks kept practicing ne waza, and naturally continued to innovate.
Technology marched on, too. It seems to me that it's no accident that Vale Tudo, the UFC, and other MMA contests that shone a spotlight on ground techniques were primarily viewed via live television and video recording. In both cases, the viewer gets a virtual "front row seat" often with video production that can choose the best among several camera angles. This makes it easier to visually understand what's going on – especially compared to a live spectator up in the cheap seats!
Defensive Handgun Shooting
Jacob Adolphus “Jelly” Bryce was a phenomenally skilled point shooter. (He was a skilled shooter in other respects, but that's not relevant here.) He developed his kinesthetic sense to an astonishing degree, practicing both live fire and dry fire in front of a mirror. The arc of his law enforcement career, starting in Oklahoma City and becoming an FBI agent, shooting team member, shooting instructor, and friend of J. Edgar Hoover, put him in an influential position. Such was his skill at point shooting and evangelizing, that his technique was cemented as the cornerstone of close-range handgun use for decades, even influencing popular culture through an article in Life magazine and exhibition shooting. Naturally, state and local law enforcement agencies followed suit with the FBI, and both populations have always been a major contributor to the ranks of civilian instructors and competitors.
It wasn't until the Leatherslap competitions of the late 1960s when Jack Weaver began to provide evidence that an improved body index (relative to a single-handed grip) and sighted fire provided better accuracy within the same time constraints. By the early 1970s, although far from universal acclaim, Weaver's stance caught on with the influential-trainer-to-be Jeff Cooper. Cooper incorporated this stance and two-handed grip into what he and others labeled the modern technique of the pistol. But it took until 1982 for the FBI to formally adopt Weaver's technique. And for that same dispersion of the new technique to permeate state and local law enforcement agencies and civilian instruction took at least another decade.
There is no doubt that point shooting skill can be developed to a remarkable degree by some. And it's possible that Jack Weaver might have developed a technique that was uniquely suitable to him, given his physical and mental skills and attributes. However, through exposure to a wide variety of students and competitive environments, we can definitively say today that Weaver's technique was easier and faster to both teach and learn, and provided results that were time- and accuracy-competitive with point shooting.
Morals of the Story
If the competitive form of a martial art (or fighting skill) prohibits or discourages a technique, over time the collective ability to both teach and execute that technique will atrophy. Eventually it may be as though the technique never existed in the system at all. You are what you measure.
The high potential of a technique alone is not enough to justify its inclusion in curriculum designed for police officers, soldiers, and private citizens. Because instructors, competitors, and exhibitors will spend far more time than their students perfecting and maintaining their skills than their students, they must be careful not to assume students can or will devote the same effort. Techniques with competitive potential that are more efficiently taught, learned, and maintained are be preferred.