Anyone have any idea why NIP-30 explicitly calls out specific kinds?

Custom emoji may be added to kind 0, kind 1, kind 7 (NIP-25) and kind 30315 (NIP-38) events by including one or more "emoji" tags

Regardless, I'm going to start supporting custom emojis in Live Chat Messages (kind 1311) from Corny Chat in the next update in addition to kind 0 and 1.