Plurality is a lot more common than most people think. The existence of pluralkit exposed a LOT of people to the idea of plurality and got them realising they were already plural. Myself included.
It's kind of like how a lot of lesbians didn't understand their own identities until they heard Katy Perry sing "I kissed a girl".
Furthermore, imagine you're on a server with 500 active members, and there are 5 systems who use pluralkit. That server has probably had the "why are you a bot" "I'm using pluralkit" conversation dozens of times. All 500 people know how important pluralkit is. On Discord, there are dozens of allies for every one system.