One thing I haven't seen mentioned at all here is the impact of this change on self-hosting. Updating apps or checking for updates becomes a real challenge with such a small rate limit. Suddenly everybody will have to switch to some mirror/proxy (or self-host one). For people running k8s clusters... good luck.
I understand Docker is paying for the bandwidth, but it's relatively cheap for them at the scale they operate. ghcr.io doesn't impose any rate limit at all (although it isn't really GitHub's main product), which I'd say proves that it's sustainable. In any case, 100 to 10 and 200 to 40 are both huge decreases and are unjustifiable for me.