Two reasons, I tend to feel that they start to feel a little sticky/nasty after I've been listening to them for a while. Also, from what little headphone experience I do have the leather cracks and breaks well before the headphones start going out. That being said, if the great headphones come with leather(-esque) pads, it's not going to make me shy away. Just a preference for cloth pads that's all.
As for comfort, prefer something that fits well and is comfy so maybe those two aren't the best bet but willing to make some tradeoffs. I understand one is never going to get the perfect set, especially in this price range.