The EN World kitten
Then the everyone loves El kicks in, goddess (singular) swoons.
Leaving aside larger issues of how much tail Elminster gets, the thing with Mystra always confused me. Mystra putting out for the people (or at least the men) whom she makes her Chosen isn't limited to Elminster; the Cult of the Dragon sourcebook makes it clear that she did the same for Sammaster when she elevated him, and it ultimately ended up contributing to his mental instability. So she was apparently making a habit of this. Why? She's the goddess of magic, not the goddess of sex (that's Sune).
My best guess is that it's a leftover habit from when she was mortal (since this Mystra was originally a human who replaced Mystryl, the original goddess of magic, after she sacrificed herself to undo the damage caused by Karsus when he tried to usurp her power), but that's still not a very good explanation.