To get my birds out of the coop I put good food for them out in a rubber bucket. I put a couple cups of their pellets, some corn, flax seeds and sun flower seeds, and then add (hot) water to make it moist. They get whatever leftovers we don't want, too. Fridge clean out day is always an epic breakfast for them. Most are excited to get up and go outside and eat. It might work for some of you to get them out of the coop.
Also, I find that just shoveling the snow isn't enough, I put down a small bit of hay (and sometimes sprinkle scratch in it) right outside the pop door, and sometimes throw shavings out from the coop if it's really icy/snowy. That also helps soak up some of the water/mud when spring thaw hits.
Just a thought.
I do have some chickens that refuse to come out of the coop all winter, and that's ok. But most do come out.