JUST THE WAY THINGS WERE
It seems that everyone had a Mini in the 1970s. That was simply the default choice.
One of the great things about having friends and colleagues roughly the same age as you is that you remember much the same stuff, and your parents more than likely had a similar car. And for most people in the 1970s, that was a Mini.
My dad’s first car was a 1965 Austin Mini Deluxe in Maroon that he bought with redundancy money