You are right, it doesn't always work, but it can work, and work really well. The way you make money is by creating volume and momentum. You buy in a low volume market, where it's cheaper to move the market, then if volume takes off and price momentum builds, you can sell much more volume without moving the market. We aren't talking about people liquidating their entire stakes, but you can make a few million here and there easy.

There is strong incentive to collude: collusion unlocks the potentially powerful profit engine of market manipulation. You make more money working together than you could on your own. If people try to screw each other too much the whole thing falls apart, as market movements are no longer predictable to the colluders, and their advantage is gone. So yeah collusion can break down in cases but as a rule people understand they make more money together

If you don't buy that theory, id recommend reading about Solomon brothers or even watching the wolf of wall st. Martin shkreli did this stuff too. I think it was Jim cramers tactic for a while (talk your book on tv, get retail volume in small cap stocks and sell into that) JP morgan and other early wall st financiers did this sort of stuff. It happens in the real world even now; I've heard from friends at big banks that they know people who will sometimes do stuff like this

market manipulation is how people make real money in unregulated markets. cornering the market is and always has been the holy grail for market manipulation and profiting in unregulated markets. It's why regulation exists. Its a theory in the same way that evolution is a theory