You answered your own question, really. From what I understand inside the studios, they're not using the kind of open source tools that are available to professional videographers and certainly not to home users.
I have talked with one person who works in computer animation, and though I won't say this is how *all* studios work, the impression I get is that the bulk of tools are in-house stuff that is under constant development. It's not being released as FOSS in part because they don't want to, and in part because even if they were motivated to do so it would be difficult at best to replicate their build environment and keep up with their development.
Also, studios are using a lot of Linux for rendering - but that's not the same as editing.
If you can point to FOSS tools that have been missed here that are on-par with commercial tools - both in terms of ease of use and power/functionality, I'd love to hear about them.
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