IRCv3 is written to be backwards compatible so it makes sense to have a ton of optional stuff - considering it is backwards compatible, everything is optional :

IRCv3 is written to be backwards compatible so it makes sense to have a ton of optional stuff - considering it is backwards compatible, everything is optional :-P. And it makes sense, IRC is already out there and has a ton of servers and clients working, you can't split that community based on the client they're using otherwise you're just creating yet another isolated chat protocol like a ton others before it.