i think it is easy to think about this in hindsight but the feasibility of a same-sex partnership was low because of the extant economic need to produce children to have help with family business/farming etc. it is only with economic security and social welfare that such partnerships become more feasible and thereby as prevalent as they are today. when the primary purpose of a relationship is partnership/pairwise fulfillment and not producing children to maintain/advance one's economic status, there are more options available.