Linux maintainers are unwilling to get rust into the kernel, so some rust folks decided to start writing a new kernel with same ABI. This allows them to make new architectural decisions. An example being their “frame kernel” (something between a monolithic kernel and a microkernel).
If I may say, it’s more legible and the tooling is way better, right off the bat.
The decision not to support GPLv3 makes sense and I understand Linus’ perspective on that. GPLv3 branched out into something beyond traditional copy left by ensuring that users can run the modified code by restricting hardware design. That’s a separate thing. I disagree with the decision to go with a permissive license in most cases including this one. Permissive licensing leads to the problems the BSDs have with companies like Sony taking the code and running with it without giving back and it’s why I prefer strong copy left licenses like GPLv2 or v3.
One other thing, yes it was rough in the past but now due to the massive market penetration Linux has we have a large swath of GPLv2 drivers making it far less of a relevant issue.