Is it usual that vets refuse to buy back unused (factory sealed and before the due date) medication after a dog dies?

When my dog died recently I wanted to sell back the unused medication so the vet could sell it to other people – certainly I had no use for it. The boxes were sealed and there were months left until the due date. However my vet wouldn't buy any of it (though had no problem taking it as a donation). If you also had a dog who died after a chronic illness, has this also been your experience? These were pills so not even something that needs refrigeration. If he bought from his supplier it would have been identical.