This can be a very deep and expansive topic, one I surely don't fully understand, nor have all the answers, but I'll try touch it on briefly and it may or may not make sense. Maybe someone more knowledgeable and intelligent can break it down for us.
First of all I want to touch on this, one of the main problems is that people are afraid to be wrong not only for themselves, but even more so posting to other people it adds an extra layer of doubt for most. Even though they know and most other people know that trading is just a probability of repeating a setup over and over and through time you're profitable. I've seen it happen, someone makes a call if he's wrong people ridicule or troll them and than they lose all credibility, over one trade lol. No one wants to bother with that nonsense, so I think that stops a lot of good traders from even attempting to help.
#1 The rabbit hole goes deep. There are so many people with tons of followers, collecting subscription or monthly fees, who can't even do a proper intra-day or swing trade. They offer very basic, standard information and make their money off the backs of others, through good marketing or salesmanship. Also, there's some pretty prominent people who are not good traders themselves promoted by in my opinion some pretty decent companies (this seems counter intuitive and not sure exactly how it happens). I could be wrong on some of them, but based on following them and what the say, the evidence as how I see points to they aren't very good traders.
#2 A lot of successful people either don't have time, don't want to help or are afraid if they teach others what they do they may over time lose that edge if too many people follow it. I don't think that's too much of a problem in reality, but in theory it's definitely correct and if enough people did indeed follow what they are doing, than it could definitely alter the effectiveness of the strategy. Again, I am not stating this is practical or even likely, but I've heard this concern more than just a little.
Well, I had more #'s planned but this could go on forever. I guess to try and just get to the point, there's so many factors at play and so many truth's that people know, that aren't really truth's it makes it difficult for people to actually come together and help each other in trading. As no one wants to put themselves out there as often the cons outweigh the pros.
It's really complicated and I probably did a poor job explaining what I mean, but I did my best.