It's because it's a weird mix of subsidies, price controls, regulations and bureaucracy that has completely distorted the market incentives.

Two things I’d think

1) the first MW is cheaper to generate than the 100th. Newer plants. Cheaper fuels. More efficient. You run your good stuff always, for peak it’s on demand.

2) the cost of the old plants are already paid for, if adding a new data center requires a new plant; may add a big cost with a 50 year payback.