No Women Please: It's Magic
When was the last time you saw a female magician perform? You will say "never". This is a phenomenon little understood. For some reason women hardly ever choose to become magicians. All magical societies may as well declare themselves men-only organizations.
Some blame the history of witch burning for this outcome. However, witch burning hasn't been done for centuries. A female in an act is commonly perceived to be the magician's assistant. This idea is entrenched and is more likely to be the cause.
When most organizations were initially founded it was in the time of male dominated secret societies. This could be a factor. Another theory is that conjuring is somehow akin to maths. Boys prefer maths much more than females. Indeed, it has been found that members of school maths and science clubs will also be members of magic clubs.
The suit commonly worn by magicians is also a turn-off for females. Perhaps they feel that an audience will not accept a skirt or dress. Magical societies will surely be the last bastion to fall in the feminine revolution, perhaps when we first see a magician wearing a skirt - unless he/she is Scottish.