As new to the TGM book and theory here's my 2 cents.
My place in the golf world is as a recreational player that strives to improve. I've played for 15 yrs now following all the traditional instruction published in print and broadcast on TV. When I stumbled upon this site I found the depth of discussion fascinating even if it was way over my head. I love technical discussion and exploration so I feel like TGM is a good fit for me. I thinks that's the main difference, some people don't have the paitience or interest to plumb the depths of golf theory that TGM does. TGM is fantastically complex to the fisrt time reader. I think that TGM is best suited to a certain personality type and the golfer at or near single digit handicap.
The similarities to a cult are apparent too. It appears to have an almost mythical figurehead, devout followers, sacred text, the handshake I haven't heard of. Similar to a religion, it attempts to answer all the concievable questions one might have about the subject with an element of faith required to boot. There's a definite sense of superiority in this forum that may be well deserved, I certainly can't suggest anything that's better and it may prove to be the best eventually.
I would not feel comfortable in telling my playing buddies to go and buy the book, they're just not that interested.
To change the perception? I don't know if it can be done without a marquee player flying the TGM flag. It sucks but that's the era we are in. We live in a world of instant gratification, something that you won't find in TGM.
Try and picture an infommercial for TGM.
My opinion is that TGM is best golf instruction manual because it properly details an immensely complex athletic activity. I am truly glad to have found it and this forum.