I wonder how well they were built.
That is, if it didn't rupture the door, could it be retrieved and used again.
If it did work, how often would it be that it would be needed? How many castles does one attack in a career? Would anyone have set it aside to be used next year ;and therefore is there one sitting around now in a museum?
If the door was really big and the petard used often; would it withstand multiple firings - I wouldn't want to be the one lighting the fuse - even if it had worked the previous 10 times.