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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.
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The market cap is a bad metric for cryptocurrencies in general and completely irrelevant in this case.
Take a look at the daily volume of the big Bitcoin exchanges. Of the outstanding ~16.5M BTC (from
which 4-5M BTC are lost irretrievably) not even a fraction is traded on the exchanges and therefore
revelant for price discovery.
E.g. Bitstamp + GDAX (two of the biggest exchanges) have a combined trading volume of
roughly 40k BTC for the BTC/USD pair every 24 hours on average (of course this increases during
periods of high volatility). This is already a low number compared to the outstanding Bitcoins, but
it is actually even less, because a trade of 1 BTC is counted as a buy as well as a sell simultaneously.
Besides, the same coins are traded over and over again by traders and bots.
I´d argue that basically ~100k BTC are relevant for the actual price discovery while the remaining
coins are either lost irretrievably or are stored in cold storage, custodial solutions and similar stuff.
Can you now see why not much money is needed to maintain a certain price?
For merely 10-20M $ (an irrelevant amount for miners) you can easily prop up the price by 500-1000 $
on a single exchange, which obviously affects the rest of the market as well due to arbitrage opportunities.
Keeping the price above a certain level is even less expensive and the miners don´t even need to
inject new capital, because they can simply refrain from selling block rewards.
Keeping up the BTC price is increadibly easy for the miners, especially when they collude to do so,
which is highly likely in my opinion.
We won´t see BTC under 1000 $ / BTC ever again in our lifetime if you ask me.