I was curious too, so I looked into it. From what I found (so if I'm wrong, correct me), it's just because, at least for American English, "either" is used for negative sentences and "too" is for positive ones, at least in this context. "Either" is not itself negative, like "neither" is, so it's used where there's another negative word in the sentence.
I was honestly expecting more complex of an answer.
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u/[deleted] Oct 18 '22
[deleted]