Debian's usrmerge
Debian has decided quiet a while ago they do not want to support different mountpoints other than /usr/ in the booting process anymore. From the origins of Unix you had the option on boot to mount /bin, /lib and /sbin) to different drives. Which made sense because disksizes where limited. Nowadays this is hardly a problem but with a history of decades it would hardly be a problem to keep it this way too. ...