This couldn't be more backwards. This has literally nothing to do with bandwidth. The kernel is a CNA, they are explicitly the ones to do this.
The reason they don't is because Linus and Greg have repeatedly, publicly stated that they don't want to because they don't believe that vulnerabilities conceptually make sense for the linux kernel and they refuse to engage in the process.
> they don't believe that vulnerabilities conceptually make sense
That's exactly what I wrote: "they have a strong belief that all kernel bugs are vulnerabilities and all vulnerabilities are just bugs; sometimes taken to the extreme in both ways".
But there is also a question of bandwidth. If a maintainer asks to bring a specific vulnerability to distros-list, the kernel security people will be reasonable. I did it last March.