These types of Visas typically require that you do graduate studies in a US academic institution to be considered "high-skilled". Nothing against this but I've seen many folks add another post-graduate degree just to tick a box.
Just guesses. I'm very curious as to the feedback loops created on the overall system.
I don't know that the word "high-skilled" is used anywhere in the actual law(s).
There is "skilled" (EB-3) and "advanced degrees" (EB-2). The latter will usually require an MS degree.