Cliff Notes version is that Ford invested heavily in market research after sensing changing psychographics and demographics in the American market. More women were owning their cars, Boomers were starting to drive, more two-car families, and a demand for sportiness (buckets/console) no matter what age.
The Mustang was the most successful launch since the 1960 Falcon.
This book shows everything that was done to make the Mustang a success:
https://books.google.com/books/about/Mustang_Genesis.html?id=2857BwAAQBAJ
Cliff Notes version is that Ford invested heavily in market research after sensing changing psychographics and demographics in the American market. More women were owning their cars, Boomers were starting to drive, more two-car families, and a demand for sportiness (buckets/console) no matter what age.