The designers of D&D are very good at creating a game. It just had to cram as many references to bygone eras and bygone campaigns as possible. Instead, it just had to tug at your nostalgia heartstrings.
So the PHB didn’t really have to teach much. And people don’t see it because most people reading the books are already gamers. Every game has crap, but for the most part, I really do love the game. On the one hand, I like the actual the game.
I have a love-hate relationship with Dungeons & Dragons, 5th Edition.