Personalities and motivations might do that and in effect produce what you mentioned.

Interesting theory. I like to say "You love who you love", but there are some interesting traits...

As I was doing some early morning shopping this morning that exact thought/question came to mind as I observed a couple that were in front of me as I was getting a shopping cart. He was rather thin and scraggly (beard/clothes), she was large and well dressed.

But as I pushed my cart through the store gathering the items on my list I noted that most couples were indeed of similar body structure or "type". IE: Large with large, fit with fit.

And BTW: the large drastically outnumbered the fit... As I have often stated here.. we are becoming a nation of "larger" people.

And please... let's not get started on the vast difference between what items were in each "types" carts...