What kind of collar?
I'm no expert, but maybe it's the collar?
When our dogs were in their puppy collars, we tried walking them, but since the collars were so thin, we clipped the leash around the whole collar, since there was no metal loop to attach it to. For some reason, the pups would give us this look like "WHY DO YOU HATE ME SO???" howl, and plop their stubborn little butts down and not budge, even with treats or petting!
As soon as we got bigger collars with proper loops to attach the leash to, the dogs loved being on leash and going for walks. It was an instant one-day transition.