[T]he issue is that you have a lot of people who are very poor at basic speaking-to-audience skills who don't realize that the number one reason the DMs they see on youtube are effective is that they are comfortable speaking *as a general matter*. A good teacher or salesman or improv actor is going to need a completely different type and degree of instruction to become a good DM because they don't have to first figure out how to be engaging in front of a crowd. People who don't have that background have a real challenge ahead of them.
This is true of many, many activities that involve social interaction - teaching, sales, management and public speaking among them. Some people are either naturally good at it, or have become conditioned to be really good at it by circumstance, and this puts them at a huge advantage in comparison to others.
I would like to christen this the Karajan Effect, after the conductor Herbert von Karajan. Karajan was one of the greatest classical conductors of the recorded era. He is probably the only classical conductor apart from Leonard Bernstein who you have a fighting chance of having heard of if you're not into classical music, and was by many measures one of the highest-selling recording artists of the 20th century. If you want to hear him in action, listen to this performance of Beethoven's Sixth Symphony and compare it with the one you may remember from the Fantasia of your childhood:
But by all accounts he did very little of what one is "supposed to do" as a conductor. He usually conducted with his eyes closed, which is considered to be precisely the opposite of what you would learn in conducting 101, because there is purportedly no way to properly communicate with the musicians if you don't do it, and he didn't particular care if his players played the wrong notes as long as they kept perfectly in time. One of his musicians said of him that "He achieved most of what he wanted through charm", rather than any sort of technique - he just made people want to play better.
You may see where I'm going with this, which is that when one thinks that somebody is a really good DM, it's often (not always!) simply the Karajan Effect in action - they're good at public speaking, performance, bluster, clarity of expression, and simply being fun to be around. This then rubs off on the players, who feel as though they are having a good time and get on board accordingly. It might superficially seem the right thing to do to copy a DM's technique if the players seem to be enjoying themselves, in other words, but you may not be able to replicate it if you don't have the requisite charm.
Another way of putting this is that figuring out what works well is not really something that you can learn from what a purportedly great DM writes about in his blog, talks about in his YouTube videos, or even demonstrates in actual play streams. Even if it is true that what he is telling you about or showing you apparently "works" for him (which I sometimes have my doubts about, especially with bloggers), that might just be because he happens to be charming - which is highly likely if, for instance, he has a very watchable and popular YouTube channel.
A simpler way of putting it even that this is: practice makes perfect, and not necessarily aping others or learning tricks and techniques.