They're offering to maintain it themselves but that's not good enough for long-term maintainers. It's like when a teenager brings home a puppy and promises to take care of it. The parents know that they will be the ones looking after it eventually.
I wish I knew of a less condescending analogy but I think it gets the point across. The list of former kernel maintainers is extremely long. Anyone who leaves the project, as marcan did, leaves all of their code for someone else to maintain. This is not a problem for drivers which can be left orphaned. For all other code it is a problem!
You're imposing your own rationales on top of CH, not expressing his own.
He expressed complete opposition to having Rust anywhere in the kernel at all, including places he doesn't maintain. He was opposed to any other maintainer deal with Rust for him, even though Robin Murphy (who is already a reviewer on the DMA side) expressed willingness to do so. His initial replies were an exercise in goal-post-moving.
The kernel is not CH's project. It's not his call to reject things he doesn't like anywhere in the kernel, including places he doesn't personally maintain.
Since Linus backed him up on this issue I’m left with the impression that Christoph is not a lone maintainer standing in the way of the inevitable march of progress; that his concerns are valid and shared by the founder and leader of the project and represent the views of other maintainers who preferred not to step into the ring on this debate.
Furthermore, the Rust code depends on his C dma code. That automatically makes it Christoph’s problem when something breaks, regardless of how many R4L maintainers come and go from the project.
I wish I knew of a less condescending analogy but I think it gets the point across. The list of former kernel maintainers is extremely long. Anyone who leaves the project, as marcan did, leaves all of their code for someone else to maintain. This is not a problem for drivers which can be left orphaned. For all other code it is a problem!