Only because they charge more for it. Their cost of producing doesn’t go up. And in general they don’t actually vary production much because throttling isn’t good on machines. But because it’s when people need to have it they get to charge more. It’s a captive audience. Which is basic economics. It’s also sleazy.
You are hugely incorrect. There are significant capital costs for installing generating capacity to produce additional on-peak power. This cost has to be reflected in pricing somehow, or you get Venezuela’s electric utility.
I am glad you are no where near capacity planning for a utility I have to depend upon.