How do you know they didn't need coal? Coal is a fantastic starting material for plastics, dyes, and many other products.
OTOH, if you expect Science Fiction to be prediction, you're looking in the wrong place. That's not what it's about. What it's about is saying "If you had these changed circumstances, how would responses be different?" There are a lot of sub-generes that look at specific kinds of responses, so whether the mining of coal was a significant plot element, significant enough that it needed to be justified, depends on details. (FWIW, I'm ignorant about Hunger Games in particular, and movies tend to be really bad at science fiction, so your criticism is plausible, but as phrased I take exception to it. I see no reason to believe that an advanced technology, even to the point of mastering generation of power via total annihilation of matter, wouldn't need coal for other purposes, or at least find it very convenient.)