That is really wierd.
I always get the opposite reaction.
When I am dog sitting my bosses BIG BORZOIS and go out and walk all of them together, my two are always ignored and people always fuss over the big dogs.

I don't think people like smaller dogs better. They are just more "portable".
I think that they think that they are easier to keep indoors. Just a guess.
I've had both bigger and smaller ones. I love them ALL!!!!