One of the main reasons why we can't replace fossil fuels is because they are arguably the most efficient way of storing and transporting a huge potential of energy.
Think about it like this. It's easier to store a ton of coal for 50 years then it is to store the same amount of potential energy as electricity in a battery. It's more efficient to transport a ship filled with coal then it is to transport the same amount of energy as electricity through power lines.
Fossil fuels have a high energy yield per unit and they are abundant.
So, fossil fuels are far easier to scale towards diverse and large energy needs compared to clean energy sources.
The author hears the bells chime, but can't find them: he alludes to the higher price of "green steel" and how subsidies are a necessary to support these innovations. But he ultimately draws the wrong conclusion.
For one, he compares Denmark to China. Which represents 18% of the World's population. Sure, if China would switch to wind energy, the effects would be massive. But that's discounting vast economic differences between those countries.