Earlier quoted context omitted.
Because coal is the cheapest source of electricity that isn't banned in the USA.
Are you looking at a textbook from the 1990s or something? I'm sure that was true at some point, but it hasn't been true for a long time.
China is building lots of new coal generation, but also lots of new solar so coal use will be reduced during daylight (not the way a coal plant wants to run, but they'll adapt)
Give it a few more years and data centers with onsite coal will look like a genius cost cutting idea. Never mind all the pollution.
[1] https://ieefa.org/resources/nowhere-go-down-us-coal-capacity...