My guess is that it's the same reason biological siblings that where separated have a tendency to fall in love or befriend if they find each other in adulthood. We are biased towards what looks familiar. Same with birds; some species have different color patterns in specimens, and it's way more common for those with matching colors to mate than the other way around. Article mentions some other documented examples. The other hypothesis, that the likeness grow, doesn't sound that good to me. Quite shallow article imo.