I have no honest answer, either.
To presume that it's due, in some part, to parenting seems self-serving, at best, though I like to believe that at least some values were instilled as the result of parental influence.
All three of my children are very similar in their clarity of purpose, responsibility, and academic achievement.
I accept that we, as parents, are extraordinarily blessed.
I cannot adequately explain it.
But I will say, and I think I've made this point before, that all three of my children scooped ice cream at that store. The store's owner was a particular and involved boss, with high standards. She was a great influence on the kids as well. Her high standards, her high expectations of all of her employees, were a shaping influence.
For that, I thank her. Sincerely thank her.
Ice cream scooper (and floor scrubber, dish washer, register operator, and the host of other menial tasks expected) isn't a career, but a first job, a teenager's job, and is a valuable stepping stone into the "real world".
Not a career, but an important experience.
I have seen parents provide their children with generous amounts of money, wanting them to "focus" on academics, and avoid the need for a teenage job to earn spending money.
I think this is a mistake. By avoiding the real-world context of a boss, work responsibilities, interacting with customers, how hard people have to work to earn money, etc., those parents who keep their children out of the work force as teenagers have deprived them of important context and perspective on work and life.
So, while I can't answer your question, I can, with absolute certainty, state that their first job was a critically important shaping experience for all of my children, and as I reflect on it, I am even more grateful for the high standards of their first boss.