IMHO..... it is because TGM is correct. Most people don't want a)to invest the time and energy into understanding what is required to make an efficient golf stroke and b) given 'a' they don't want to be told they are going in the wrong direction. The book stands as a constant, unchanging reminder that an individual is or isn't doing something correctly. What percentage of people in our society take responsibility for their failure? 100% will take credit for their success.
The book requires a certain intelligence to understand and that intelligence isn't minimal. AND... it requires a lot of time to even begin to master. Not everyone will make that commitment.
Now, as to why so many people think TGM is a cult etc.? Again, imo, that is just the way the VOCAL minority behaves. If something is hard, and requires work.... don't do it, just criticize it. I read a post on GEA where the nut poster actually equated TGM with a religion. You can't argue with people like that, you surely can't reason with them
.... just ignore them . (BTW... the same nut challenged Ted to a golf match, for money, and I think he is a 6...and probably a vanity 6... and probably can't hit it 230.) We shouldn't get too sensitive when dealing with people like that.
I'm not sure TGM is misunderstood at all. Those with open minds who try it, and work at it, know it works. They know it is unchanging and that the principles upon which it is based are factually correct. Those who have a vested interest in TGM failing or who are ignorant and prefer to stay that way will criticize it. They will follow the instruction found in golf magazines....I laughed recently, I have a complimentary subscription to one (don't remember which one) and in the last issue there was a world renown instructor telling everyone to use the right hand to control the clubface..... I'm dying to see how many people get messed up on this one.
Ultimately TGM will succeed because it works. Many other well marketed, highly financed products that don't work that well will also succeed, at least financially, and at least for a time. This happens often in service industries. I think people who teach and promote TGM need to be patient and less sensitive. Everytime I see someone who doesn't think TGM isn't correct, I just think "there is another guy I can beat." Now, to be truthful, that isn't always correct, because there are some people so talented that they don't even need instruction to play at a higher level than I'll ever be able to play at.... but most of the time, it's true. Focus on those that want to learn and don't try to convince anyone. Word will spread and people will follow results. The one thing I would recommend is staying away from hostile environments. There is nothing to be gained by arguing with the Stags, Hammers, and george hibbards of the world. You can't change their opinions, they aren't there to have an exchange of intelligent opinion, they're there to fight.