Although there are "experimental" labels on features in the kernel, there's no coherent definition for what that means. Historically most distros have enabled CONFIG_EXPERIMENTAL features by default, until the flag was deemed meaningless and removed. Linux has never removed a mainline-merged feature this quickly. Features in staging may be removed quickly, but bcachefs was merged into mainline. The bcachefs removal, not to mention the removal timeline, is unprecedented for a mainline-merged feature. There's never been any expectation that experimental means it may be removed on short notice.
Going forward, I'll agree with you: mainline does not care about users of experimental features. But it's disingenuous to suggest that this has always been the expectation.
Going forward, I'll agree with you: mainline does not care about users of experimental features. But it's disingenuous to suggest that this has always been the expectation.