This, this, this, a thousand times this.
I have only been GMing with this edition, since 2015. Learning how to GM is/was very difficult, and is a perishable skill, especially early on. Figuring out how to balance different player expectations, the nebulous rules of exploration and social interaction, when rewards should be given out, and how to pace the game should be done for me in the DMG. I shouldn't have to go trawling up youtube videos, hopping on tiktok, or digging into 50 year old forums in order to run the game.
Almost every single RPG in print right now indeed suffers this same flaw.