Yes, the sanctions against Russia, as mentioned by Linus. The change also said the maintainers “can come back in the future if sufficient documentation is provided”.
My guess is that the Linux Foundation must ensure that none of the people they work with are in any way associated with any organisation, person or activity on the sanctions list. And that they preemptively removed all maintainers that might risk violating the sanctions while they work with them to establish whether they might be covered by the sanctions or not.
Regardless of what you or they think of the sanctions, they are the law, and I don’t think anyone wants the Linux Foundation to have to spend their money on lawyers and fines because they had a maintainer who also worked on a research project funded by a sanctioned entity. (If that is how it works, IANAL)
The massive negative outcry over this fairly uninteresting change certainly seems oddly overblown, almost as if there are parties trying to turn it into a big political issue to paint Russia as a victim. But idk, nerds freak out over stuff all the time completely on their own.
Giving them the benefit of the doubt, I think the Linux Foundation has a hard time being clear on the matter because it just isn’t clear. These are new laws and a global open source cooperation run by a non-profit is likely a corner case that the lawmakers did not think about at all when making them.