Remember a lot of bears are pretty small. Also, if they find a sleeping one they can’t just snap out of it on a whim, they are pretty helpless. We’ve knocked into a few pheasant hunting in December/January in MN/WI and also first spring turkey seasons or shed hunting there too. Some are so dopey you could put a dog collar on them. I’d bet the wolves that do it have expertise and a pattern. Like orcas that specialize in seals on the beach or washing them off icebergs. Specific, specialized learned hunting tactics that are handed down within the pod/pack. From their standpoint a winter bear is a pretty big meal during a tough time to find calories. I’ve never seen a kill or seen it happen but have found wolf scat in the spring out beaver trapping when ice is still on in Mn that had really long black fur in it that I supposed would have to be bear. Just one time.