For different reasons.
Some men seem to think that small dogs will "ruin" their image. This happens quite often. And, these men are often composating for something. Who knows what. These men are usually the men who go out and get those overbred, ugly (i love dogs, but they ARE ugly) monsters of rottweilers or pit bulls or mastiffs. While I love all three of those breeds, the overbred ones are just... yuck. Then, there are men who simply can't admit that yorkie or a chihuahua or a papillon would make a better companion for them than a dogo argentino. (my brother in law is a man like this- he thinks an American pit bull terrier is "his" breed; however, I've seen him with our chihuahuas and honestly, they are the PERFECT companion for him- after all, he likes his dogs cuddly, playful and feisty) There are also men that simply prefer rough housing with big dogs over small dogs. Can't blame them. It is fun roughhousing with big dogs.
Personally, I think the whole "small dogs are for girls, big dogs are for boys" thing is a bit sexist and stupid. A dog is a dog. Some big dogs make GREAT companions for girls and vice versa. I have a saying that I use all the time...
"Silly girls, small dogs are for boys!"
