Well, as for teaching by showing, I have noticed something in our schools. I am only one generation of student down from the original Master that came here from Korea. When he arrived, he didn't speak English. So, when he taught, he showed them by doing, by demonstrating with his hands, by hitting the offending foot with a shinai, etc. He couldn't verbalize the techniques.
I learned white to black belt techniques from one of his original students. Luckily, he was very good at conveying the techniques verbally, which made him a great teacher. When my teacher moved on, I was absorbed by Grand Master's school. Learning from him was much more esoteric. Now, by this time his English was vastly greater than 30 years ago when he taught my original teacher. But, at times he still had to demonstrate by showing or doing the technique on you. Still, he always tried to explain. If he couldn't he would come grab your leg and twist it for you. He'd move your foot from that position to this position. It was never just "watch me and replicate".
So, my theory is that you might still see people teaching without explaining becuase that's all they know. I'm sure there are some students that learned from non English speaking Masters that didn't get much explanation. This either by design, becuase he didn't feel the student was worthy, or simply because the teacher didn't know how to explain it. So, they might try to teach that way becuase they think that's the thing to do. This is only becuase they never saw anything else. In short, students are always a reflection of their teachers. Combine that with one of those people who just inherently are not good teachers and you could wind up with this situation very easily.
There are no PERFECT techniques, only perfect execution for the situation at hand.