Men can't purchase something that isn't there. I've talked to plenty of male SL players and they lament the fact that they can't easily run out and buy clothing they like, like I can. They end up wearing the same outfit for 6+months, simply because there hasn't been anything they've liked that's been released in that time frame. Even stuff that has been released, the quality isn't always good.
The men of SL aren't really given the wardrobe choices they should have. In another thread, several months ago, Skell gave examples of clothing he'd love to see in game. Several people expressed interest in them, but guess what? No designer has come out with anything even remotely similar. I, for one, would buy men's clothing for gifts. I've done so before. The holidays are coming up and people will be spending Linden left, right and center. But, they can't buy what isn't available.
If guys were given more clothing options, chances are good that they'd actually spend money on themselves.