Because mined coal can be burned in order to produce electricity.
Also, none of these strikes would have happened under a Labour government. As usual, I blame the Tories in the liberal party.
Lets say the price of electricity is 1 per unit consumed.
A mine can produce coal enough to produce 100 units of electricity.
They hire 10 workers, who each are paid 10 cash in wage per day.
So the mine is producing 10 units of electricity (in form of coal), they are sold for a sum of 100 cash, which is all used to pay the wages of the 10 workers, who get 10 cash each. The mine is making no profit, but neither making a loss.
What happens if new sources of electricity are introduced, like nuclear power, or wind power? What if foreigners produce electricity more cheaply?
The mine will start making losses, all other things being equal if the price of electricity drops.
They either drop wages or close because they cannot operate on the long run with losses.
Simple logical conclusions. So why keep the mine operating, if current factors of production make it unprofitable with current wages?
You can hope you get new technology, so 5 guys could produce the same amount of coal that 10 guys used to.
If however, a government starts subsidizing the miners to stay employed, it only means that the mine is still making a loss, but the one who pays for the loss will be the common man.
Meanwhile the workers could have found more profitable jobs, that would not have to funded by the common taxpayer!