I’m talking about actual moulds not designs for a mould. The expense is in the actual physical creation of a mould that one can then reuse in mass production. Having design files for one of the freely-available (to manufacturers) public moulds wouldn’t necessarily do one much good as you would need the actual physical moulds and all the infrastructure behind it to make a case.
Granted I’m by no means an expert in this part of the process, this is just my limited understanding.