As with so many things, because vikings.
In the Germanic and later Norse belief system, magic - seithr - was believed to be 'argr', or inherently unmanly, so most practitioners of magic would be either women or inherently untrustworthy. The one exception is Odin, who went to great lengths to learn the secrets of magic, but even he gets called out as being a bit sus for having done so. This gives us a mythical framework where there's at most one 'good' male magic user, and the rest are either women or scoundrels. Cross this with another element of Norse mythology - the dokkalfar, or Dark Elves - and you get the inspiration of the Druchii, with the one 'allowed' male magic-user of Malekith and the rest being women or condemned outlaws. There might have been a detour along the way into the Drow of Dungeons and Dragons, and their Spider-Goddess Lolth might be why Hekarti has six arms.
The vikings go west. The Arthurian mythos were originally a mythologization of the post-Roman Britons - largely Romanized Celts - resisting the incursions of Germanic Anglo-Saxons, but over the years of the English melting-pot mixing the two together and then receiving further Norse infusions via the Danelaw and the Normans, the myths picked up a lot of additional cultural influences that would eventually feed into the Bretonnians. This is how something predating the concepts of knights and chivalry becomes very much about about knights and chivalry. The mad Welsh prophet Myrddin became the mysterious, wise, magic-using, and overall very Odinic Merlin, and since him as the one 'allowed' male magic-user didn't make it into Bretonnia, there are none, only women. You could use most depictions of Frejya, the Norse Goddess of (among many other things) Magic, as a picture of the Lady of the Lake or a Bretonnian Damsel.
The vikings go east. Kievan Rus becomes a cultural melting pot of Norse and Slavs. The myth generally known today as 'East of the Sun, West of the Moon' goes with them, becoming the Russian myth of 'the Bear-Husband' and eventually inspiring Hans Christian Andersen's Snow Queen. You also get the Norse beliefs about seithr mixing with Slavic ones about shamanic magic or volkhv to create the incantations and enchantments of zagovory. This was not necessarily a feminine art back in the day, but one of the few traces of it to survive centuries of suppression under Orthodox Christianity is the legend of Baba Yaga. Put all that in a blender and what you get out is the raw material of snow and bears and witches from which Kislev was made. What you don't get out of it is any male magic-users.
