Some (most) of those cars "Overhauled" on the show were worn out POS rust buckets when the overhaulin show got them. The owners neglected and drove them into the ground and let them get in that "I'll get around to rebuilding it someday" condition before the overhaulin crew got them.
Why is is such a stretch to think those same owners neglected those same cars after they were rebuilt for them for FREE.
Those are classic cars, with some high end components added to them. They will require some maintenance to keep them in top condition. What are the odds that those overhauled cars aren't getting that maintenance? They didn't take care of them before, why expect them to now?
Probably more like they are just being driven until they quit again.
But the bottom line is this. WHATEVER overhaulin did to repair and restore those vehicles is more than they ever would have gotten from their owners.
Most of those cars would still be worn out POS rust buckets, sitting under a tarp rotting away if overhaulin hadn't came along and rescued them.
I'd let them do one of my cars in a heartbeat.
But I'd go over it bolt for bolt when I got it back...