I assume that they sign up to long term contracts to secure the price of power.
When it comes to renewal, the DC operator obviously has a sunk cost that they don't want to walk away from. But the electricity generators are also in the same boat. If the DC shuts up shop then there's x00 MW that the generator won't be able to sell and could suppress prices across the whole country. So both parties are incentivised to come to an agreement.