Exactly, if you build a coal power plant today, the LCOE is calculated assuming the facility will run, let's say, for 30 years at 80% capacity.

But what happens if you have to stop your power plant in ten years because its (LCOE-estimated) cost is not competitive anymore?

So based on an biased LCOE computation, you sold your coal-based kWh at a third of it's real cost. Bad for the investor, bad for the climate.