I have a few theories...
All I can say for sure is that there is either a genetic component (nature) or the psychological/experiential component (nurture) must have happened very early for me. I was very attracted to strength and muscle in girls long before puberty even hit. I can distinctly remember getting girls to flex their biceps for me or arm wresting or give me piggyback rides in kindergarten and 1st grade if you can believe it. I didn't know why I was compelled to do it then either, all I know is it gave me an incredible dopamine surge and made my head spin like nothing else would. It still does 40 years later. I couldn't change this abput myself if I wanted to, it runs right to my core.
I don't know why I became attracted to muscular women.It was in the 70's when I saw Laura Del Rio in an edition of Wrestling Review and it just clicked.She was fit and well built by 70's standards but by today's standards she would be consiered pretty tame.Since then I have always been attracted to images of strong muscular women.