I think "back in the day" the hardware and software for doing VFX was a lot more rare and expensive, and often more customized. So it may have been more appropriate or made more sense to credit those companies. For example SGI (Silicon Graphics Incorporated) was at one time one of the *only* vendors of high-end VFX-appropriate workstations. Some of those companies may also have been making marketing deals to get their names into the credits, which is not really affordable for a small company. I don't know for sure what happened, but those are some theories/ideas.
- Oshyan