This is a game played by friends, right? The nerdiest one in the group buys the book and invites everyone into a cozy basement for a few hours a week, right?? Well, yes! That's one of the beautiful things about TTRPGs - friends telling stories together! That's why I'm always happy to help other GMs get their start.
But that's the trouble for newbies; without a coach, it can be exceptionally tough to get started. So much institutional knowledge pervades the hobby that even experienced game writers can find it troublesome to convey all that, without overwhelming the reader. It’s like learning to drive: sure, you could learn how to drive by reading a lot about it and then getting behind the wheel… But the learning process is much smoother with an experienced member at the table. Someone who can give pinpoint instruction when the information is relevant, rather than a deluge at the beginning.
There are also benefits for experienced groups! I consider it an honor, a privilege, and a professional development to watch other GMs at work. There are so many ways to give a table a great experience, and I’d be a fool to think I know all of them! There’s also the simple matter of fatigue. Some GMs want to play, too! Your home GM deserves to kick back and play their own character sometimes. Trust me, they can get tired.