@elfin Well, WordPress already supported multiple users and multiple sites, before WordPress MU. So the naming is clear as mu-d to me.
I’m assuming MU “merged” with WP because the core code grew and became more adaptable, ultimately superseding MU’s raison d’etre. Did this factor into the name change? In the process, did “MU” morph into something else, chang direction, change focus?
Maybe calling people “users” is no longer fashionable?