Well, that is a good point. No the load isn't 100% constant but it's much more constant and they're using way more energy than a residential user so the "bulk discount" thesis still applies

For DCs doing training, their load is constant as long as training is happening. But as soon as they end a run, their load can disappear quickly. This is actually a problem, as the grid and generators are not designed to see massive amounts of load go away instantly

Several system operators are working on new guidelines about these large loads, and they're working on ways and regulations such that these loads have to ride out grid instability and not just disappear without warning

They can fill the rest with offline tasks like batched API requests and training.