Because it's not a "hard" E.... it's a mid-central vowel in "foreign" (schwa): https://en.wikipedia.org/wiki/Mid_central_vowel (like when going "uh")

Proof in an American dictionary: https://www.merriam-webster.com/dictionary/foreign

While "ei" in "Neighbor" is NOT a schwa, it's an "ay": https://www.merriam-webster.com/dictionary/neighbor