I have this problem. A couple of AAA projects I worked on, years of work, got cancelled and all that exists now is "stolen" footage. Then there's the dozen mobile apps that have been pulled from the app stores (or gotten "out of date" and no longer supported). Can't find APKs or store listings, just 3rd party site reviews are the only evidence of their existence.
Probably their contracts forbid them to, so even if they save something, it is practically piracy anyway.
Most code written by software engineers work the same way. The code is owned by the company, the employee can't keep any of it after you leave or is fired.
The credits couldnt theoretically magically appear?
I mean they wouldn't be infringing on copyright or whatevs since they are just a list of names. and additionally most people on these lists would corroborrate the existance of most other people there (which doesnt make it perfect, but better)