> […] why would they sell bitcoin to continue funding their mining operations […]

There are usually some fixed costs involved and you need cash flow. Without cash flow, your business can shut down pretty damn fast. With cash flow, your business can stay around longer, maybe long enough for the economics to shift.

This sort of thing happens with oil. There are oil producers which sell at a loss. There was even a brief moment when the price of an oil barrel went negative, which meant that if you gave somebody a barrel of oil, you had to pay them for the privilege of taking that oil off your hands. Oil producers did not all shut down when that happened.

I am a little doubtful of the $19k figure anyway.

> It would actually make more sense to sell all their bitcoin, flood the market with coins to do the price, wait for large miners to collapse and then restart mining at hopefully lower prices.

This kind of market manipulation is not so straightforward.