You forgot two other reasons-

Extra pockets;

They look really outdoorsy and manly.

Seriously, I have two-a lightweight fleece I almost never wear and a thin fiberfill of some kind I bought here cheap. They aren't that warm, but I do like the extra pockets. Neither one goes into the backcountry with me. For that I wear a fleece jacket and if colder, a down jacket or the big parka in my photo. A big puffy vest would be nice in some situations, like over my ski suit while riding a chair lift, but not at Patagonia or TNF prices.