While Matt is technically correct, it's much easier to maintain a conspiracy like this when you have a small number of participants with a high concentration of share.

If power is more diluted among a greater number of participants you are way more likely to see defectors, which would provide accurate pricing data to the market and cause the conspiracy to fail.

Can that be reduced to Prisoners Dilemma game theory?

Or even better, folks actively trying to screw the market manipulators.