Because Discharge is a weak T-Bolt and Charge and Nuzzle have different effects.
If that effect is too similar to be put on the list, then how did Thunder/Thunderbolt make it on? Thunder's just a stronger, less accurate version of thunderbolt.
Because both Thunder and Thunderbolt are both viable in singles, whereas Discharge is only used on pokemon without T-Bolt. --- My AC:CYOA: http://www.gamefaqs.com/boards/997811-animal-crossing-new-leaf/68964849