The lock might be broken? Gummed up lubricants come to mind. No idea if that's a common problem with safes, but it's pretty clear that a safe would not have an

The lock might be broken? Gummed up lubricants come to mind. No idea if that's a common problem with safes, but it's pretty clear that a safe would not have any outside maintenance access to fix a problem like that (other than drilling it open, which seems to be routine enough given the "yeah, we can make it usable again" offer)