While I agree we should try, there are simply cases where the migration was impossible to revert, simply because the data no longer exist. I don't recall a time we'd actually need to rollback in core, but I agree this should be standard for plugin maintainers in case users want to uninstall the plugin.

Now, the reverts are failing for wrong usage of `up` vs `change` usually. The goal is not a time travel and revive historical data, but make the foreman able to downgrade version or two and still be usable.
It's common that, data migrations have only `up` method :)