Yea, it’s pretty funny. It used to hold the home directories, but the disk holding the OS ran out of space, so they started putting new utilities in /usr/bin. The distribution tapes they sent out to everyone who ordered a copy were made directly from the live system, so we all inherited the same quirk. We’ve moved the home directories elsewhere, and now the whole OS is climbing into /usr in order to be atomically mountable. I keep thinking of that Gilbert and Sullivan song with the line “it gradually got so!”.