the question is too reductionist and over simplistic
there are cases when people who have NOTHING in common can fall in love and make a relationship work..........has a lot to do with the individuals involved
and in other cases, people look for those of the same ilk
if you think about it though, how many married people are into the same shit..........he golfs she coaches cheerleading............ he doesd fantasy football, she is in a book club
being into the same things isnt all that important.........
but with people into fitness, it is kind of important to find another who is into that lifestyle