In the innocent early '60s there was a sentimental pop song, a duet between "Paul" and "Paula." I think all wholly or partially Latin-derived languages have some given names with masculine-feminine variants. But why only some names and not others?
There actually aren't that many male/female analogs in English-speaking countries: Robert/Roberta, Martin/Martina, Frederic(k)/Frederica ... but the feminine forms seem to be in increasingly rare usage. Edwina is virtually obsolete. (So is Edwin, come to think.)
French and Italian have many more unisex names, usually created by an "e" ending in French (Daniel/Danielle, François/Françoise, René/Renée), an "a" ending in Italian (Carlo/Carla, Francesco/Francesca). I'm not sure what the story is with Spanish but my impression is that there are lots of paired names.
Yet, as far as I am aware, neither English nor French nor Italian has a female form of Jerome, Ronald, Thomas, Peter (although the Germans have Petra!), William, Samuel ...
Speaking of Francesco/Francesca: Francis has fallen out of favor as an English name, but the French and Italian versions are still serviceable. The French name some of their offspring François/Françoise, the Italians Italo/Itala, but no Americans however patriotic name their kids Americo/America.
Sandro is an Italian man's name (as in Botticelli), but Sandrine is a French woman's name.
That's the game of the name, I suppose.