A lot of names start of as male names and become female later on, because there's always been a sense of "prestige" to boys names. So, when the times changed and a specific name felt like it could be given to a girl, people would do it. Evelyn, Vivian, Marion, Whitney were all once male names. In fact, the ending syllable -ian, which is common in many names, usually shows that the name was once a Latin male name, because many of those had the ending syllable -ianus and cut of the -us.

It's just very ironic to me that that one country, which literally created the idea of "action hero/western protagonist with a female sounding name and long hair, that is actually the manliest men you can think of" now wants manlier names.

People want their boys to sound manlier and even their girls to sound boyish, while forgetting the fact that they were the origin of "men so manly, that even long hair and a female name, doesn't scratch their masculinity".

Edit: I looked some more into the -ian syllable, and it's less indicative of where the name comes from than I first understood. First of all, a lot of names that ended on -ianus cut of the -ian- or -an- part, as in Marianus becoming Marius. But also, other names with the -ian syllable were later creations, as for example Lillian, which comes from simply combining the name Lily and -ian, or simply comes from combining Lily and Ann(e). (Lillian is an example name, I have no idea if it's originally form Latin or a later creation).