Sit down restaurants still have lunch pricing now. Lunch is generally a smaller portion, not a lower price for the same thing.

Fast food has been priced the same throughout the day as long as I remember.

This is neither of those things. This is pricing based on current demand and charging more for the same thing just because other people want the same thing. For fast food, higher demand is generally better because the ratio of income to staff is higher than during slow periods.

This is horrifying.