Do you really think that if mining becomes unprofitable he will simply call it a day? After all it could
only be unprofitable for a short time if the price rises again. He is heavily incentivized to prop
up the price and so is every other miner, who would be in the exact same situation.
They can be incentivized as much as they want, it doesn't matter. Bitcoin market cap is $146 billion. I don't know how much they have invested or how much they are willing to invest to pump the market, but I still think it is a drop on the ocean. Please explain how else they could pump up the price other than buying bitcoins and how do you come to the conclusion that they have enough money to pump the price.
And if the power costs are higher than the reward, then it is a no-brainer: E.g. electricity costs $1 million per day. Reward is $900k a day. Then they lose $100k per day, if it runs, but you make $0 per day if it is shut down. Of course, it might be not full-on / full-off, they might try to keep running half of it, and if everyone does it, profit still gets positive, but it doesn't matter for the price.