The cost of "unions protecting their job" increases further as the alternatives get cheaper over time. So it's not sustainable in any way. Additionally, fossil fuels are usually subsidized the most in local areas where they are mined/extracted so states/regions with no such natural resources can be expected to move way faster in adopting new forms of energy production.
While the UMWA certainly has a vested interested in keeping coal mining jobs around, blaming unions for protectionism here is a little far down the value chain.
