Can you PM me an email, please? I have loads of info on the subject that I can send. There are no certification standards for runway width, BUT, FAR 25 does have standards for Vmcg and performance planning, meaning a prudent operator would not regularly use runways as narrow as 75' without applying some mitigations. Crosswind and contamination limits usually. I'd ask what is the FAA's justification? See FAR 150 Civil Airport design. Especially any Advisory Circulars pertaining to runways which is as close as you will get to an answer.
GF