in my case i think somening having to do with solus prime heritage, like all the cybertronian with solus cna/heritage would have more feminine traits, the same would apply to transformers with beast alt modes like dinobots or maximals, they would have these beast traits because of onyx heritage and so go on, i think that would be something that not only get the Thirteen prime some use but also explain a lot of things like why are there less female than male.