Archive-by-VM has been attempted from time to time. In the case of VFX there isn't a single server, but many different workstations, servers, render blades, etc. So preserving the entire pipeline in amber is a challenge.
And, somebody has to pay for it. The producers of the current project won't allocate any of their budget to preserve something for a (hypothetical) future sequel/re-release - that is somebody else's problem. The only places that I know of that do a decent job with archiving are animation houses like Pixar that own their own IP.
