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For the same reason the Referer header is misspelled in HTTP - because life can sometimes be that way. https://en.m.wikipedia.org/wiki/HTTP_referer https://en.

• dmurray 9y ago
  Interesting, "referer" always looked believable to me as an alternative spelling from American English, by analogy with the likes of "traveler". But apparently not, because the accent is on the syllable that would be changed. I found some answers about exactly when US and UK English differ on this point, though none of them is comprehensive: https://english.stackexchange.com/questions/9192/cancelled-or-canceled https://english.stackexchange.com/questions/9192/cancelled-o...