If I knew something about the stock market that was valuable and I told people for free i would destroy the value of that knowledge.
Thus 'those who know don't talk and those who talk don't know'.
This is math and you can't get around it. By definition somebody pontificating on the stock market is doing it for self-aggrandizement or to fool you to make bad trades.
It is a minefield though and you should never 100% trust one source on any given investment, but to act like there is some kind of mathematical truth that no one ever publishes any useful stock analysis is just silly.
For instance, suppose someone said that many if not most people could be very successful investing if they just skimmed the description of each public company's business in the 10-K annual report, and chose a small number of the best ones only after reviewing all of the thousands out there.
That's way too much work for most people, but it's hardly impossible. It's not even a full time job.
But given it's not attractive to follow that procedure, telling people they should do it has no noticeable effect on its value, even if it works.
Not if you've taken your position and then encourage people to realise the same.
E.g. A more extreme example, but sometimes you see people up dirt on a company showing how they are fiddling numbers/debt etc, take a position and then publish.
Also realistically (more extreme examples aside) you telling the world what you know about a company wont change diddly, but just acts as a sounding board or because you like to announce/discuss it.
Now there are no absolute certainties, and the knowledge that come close to absolute certainty and aren't publicly known, are usually pretty illegal to share.
What's left it mostly speculation. Which is fine, that is how this all works.
The "dollars get left on the floor" because the opportunity is limited there. At my local track I'd estimate that a bet more than about $50 would move the odds into a bad place for me. If I have a big bankroll I can't make Kelly bets anymore and my rate of return goes down. People who are good at this and serious about making money start their own sports books, trade derivatives, or something.
(Don't laugh I sold half of the stake for $1200 a few months later. It has been up and down and I haven't looked at it for years but the other half is worth about $1500 right now)
It's true that you can't move AAPL that way but there are many things about trading that I didn't understand before I adopted a few penny stocks where I can see all the trades.
Move the stock higher, peddle it on /r/wsb, sell your position, buy up shorts?