Why is the root partition not remounted rw after booting is finished if mounting other disks fails?

I have a Debian 12 server that I just restored to a different hardware from backups. The new hardware is missing some disks and of course they failed to mount. After the machine booted, the root filesystem was still mounted read-only. I checked everything, but didn't find any issue. Then I removed all the *.mount services for the missing disks and the server booted with the root filesystem mounted writeable. That makes no sense to me. Why should the root filesystem, which is completely fine and without any errors, not be mounted rw if any other mount point fails? Is that a behaviour that I can configure somehow?