Why "Peanut Sauce" is known as Thai Food

[Northern]

I find it funny that "Peanut Sauce" is everywhere in the west and seems to get more popular. People always refer it as "Thai" and many believe Thai food is all about peanut.

If you go to Thailand, ask them about peanut sauce and most will go blank. They don't know what peanut sauce is.
Thais put ground peanuts, as just another ingredient, in so few dishes that they don't consider peanut a main ingredient of Thai cuisine. And peanuts are coarsely ground so that they're like thick grains of sand, and not mud or peanut butter.

Why is it like that?