Someone is doing Don Kanoji! Sweet! I know what expansion I want to get first!
I'd assume so we don't have 50 different versions of the same character running around. There are some characters with a ton of moveset potential, and it would simply be chaotic to have all of them running around. Better to leave expansion slots for other characters.
If I were you, I'd ask to work with the other person on a group expansion for that character. This way, you both can be involved, it only takes one character slot, the expansion gets done sooner,
and I get to play as Don Kanoji either way. and everyone's happy.