Try to ASK HN: Why don't airlines have to display a price list?

In my country, shops are required to display a price tag on every single item or face a fine. I think this regulation is in place to protect buyers from scams and ensure fair treatment, anyhow I like it. However, why airlines do not have to follow this same requirement? I'm curious to know why this is the case. Can anyone shed some light on the reasons behind this evident exemption?