Why don’t changelings reveal themselves?

I am preparing to run my first Changeling: The Lost game and just read over the rule book. One thing I don’t understand is why the mortals don’t know about the Changelings.

Vampires have strong reasons to hide from the mortals. The mages in Mage: The Awakening would actually have a hard time revealing themselves even if they wanted to. But Changelings can reveal themselves to mortals (p. 108). There are some negative consequences to doing so, but those consequences are primarily supernatural in making it easier to track the Changeling. I haven’t found anything about the mortals forgetting or rationalizing a changeling that has scoured her mask or overt use of contracts. In, fact there are some advantages to forming a contract with mortals and the types of contract discussed might involve the human knowing the changeling is at least somewhat supernatural.

I see plenty of reasons an individual changeling may not want to out themselves specifically, from the risks of attracting the Huntsmen to changing relationships she doesn’t want to change. But I don’t see anything preventing the world from knowing about the existence of changelings in general.

So, why don’t the mortals know, at least in general terms, about the existence of changelings and the True Fae?