Frequent lick spots

Hey vets! Question, my cat and my brothers cat (living separately) both get these bald patches on their legs from licking too much. Both cats have been to the vets multiple times, both got steroid shots, bald spots disappear, and then after a month come back. I really can’t afford to keep spending $200/month on vet care for the same wound to come back. I’m curious if anyone knows the reasoning for this, or has any suggestions?