Strictly because the tooling doesn't exist in an easy enough way to go from blu-ray -> full-sbs encode at this point.
I'm constrained by knowledge to only use tools like BD3D2MK3D to create full-sbs encode in x265 which I watch in VR.
If AV1 were an option in this tool I'd consider it, but the additional encoding time might not be worth it to me as the person actually encoding the files.
If anyone has knowledge of F-SBS or F-OU AV1 content or tooling please let me know as I'd be glad to learn.
Preventing the updates is also another benefit of airplane mode if youre planning to jailbreak the kindle eventually.