Men would feel their masculinity is threatened - having to be seen with all those elves. Men don't answer their mail. Men aren't interested in stockings unless somebody's wearing them. Ho Ho thing would seriously inhibit their ability to pick up women. Finally, being responsible for Christmas would require a commitment.
Cupid flies around carrying weapons.
Uncle Sam is a politician who likes to point fingers. Any one of these individuals could pass the testosterone-screening test. But not St. Nick. Not a chance.