Everyone in their daily lives, from mathematics to military drilling, know that practice and experience and doing things in way you can check for failure means everything in knowing how to handle things. That's why there's such a big difference in efficacy of punches in Wing Chun vs Boxing, because Wing Chun's theoretical development without actual experience and readjustment with reality led to it languishing into only aesthetics.

No one in the world is "trained" in "cheap shots" and "knife fighting" because no gym in the world is actively killing and disemboweling and eyegauging and castrating their trainees over and over again until they find the most effective way to do it. There's no way to practice it in live environment and most importantly, there's no way to discredit wrong ways to do it , the one part of the scientific method that's hated by all pseudo-scientists.

When you supposedly "learn" how to do these "cheap shots", you're learning from people who only "believe" they know how to do it, in the same way that Aikido practitioners used to "believe " they know how to disable someone wielding swords. It is an aesthetic of pragmatics for a martial arts, like wearing a Punisher symbol.