Suppose that one guy have 31 million dollars, he bought all the 21 million coins at $1, and sold 10 coins to others. Then, he still have $10 million at hand. Then he refuse to sell any coins below a market price of $1 million and are willing to buy any coin at a price of $1 million. Then bitcoin's market price will be $1 million
He can set a bid and ask price, but he can't force anyone to trade at those prices. Suppose nobody will buy at $1 million. There will be no trades so you don't know what the market price is.
Also, if he was able to buy up all the coins for $1 each, then obviously nobody values them any higher than that. In this case, the owners of the 10 coins will happily sell them all to the rich guy for $1 million each. They have $10 million and the rich guy who started with $31 million is left with 21 million coins that he can't sell.
In reality there are so many different people with different psychological qualities that there will be someone to buy and sell. Just look at the variety of stuff people collect. And for people to trade in milions we would have to spend some time on 200k, 300k and so on. Which means a guy who traded the market at price range of 800k-900k for 10 years wouldn't be as startled of a 1 mil price as we are now.