One of the problems is that states are very liberal in their awarding and renewal of these placards. My husband applied for a placard in PA in 2006 after a knee injury. He had the choice of 6 months or 5 years on the placard. He used it for about 2 years while he was on crutches and rehabbing his knee. Then he forgot about the placard until the automatic renewal arrived in the mail. While the initial application required a doctor’s signature, the renewal did not. I think many people end up with placards for life, long after a short-term need has ended. Similarly, when my aunt died, I found placards for Florida and New York in her car. She had a legitimate need, as she had a prosthetic leg. However, there is nothing except conscience stopping me or anyone else from using them now. I doubt any parking authorities are checking the identification numbers on them against death certificates.
But I keep mom's placard in my glove box for picking her up. The other really weird thing about some parking lots is the relative abundance of disabled parking places relative to the small size of the parking lot. I must confess to misusing her placard once when there were eight disabled spaces open in a lot where every single other space was taken. This was a small strip mall, not the type of place where you'd expect physically disabled people to congregate.