In the short term, flexible power production like coal generation gets used to satisfy grid demand during situations with abnormally high power requirements. It has the benefit of being able to be turned on and off practically instantly. There is no economic incentive to build out sustainable generative capacity if it won't be running all the time, and balancing the load on renewable power is awkward (see power price rate inversions for examples of utilities paying people to use excess energy).
I remain unconvinced that cryptocurrency is long term detrimental to clean power generation infrastructure. Quite the contrary, the existence of cryptocurrency to mine acts as a 'productive' sink for power produced in excess of grid baselines. In practice, our entire grid could be renewables in excess of peak demand, and cryptocurrency mining a flexible network load. It could quite possibly get us off of non-clean energy entirely.