It's about lorePrideful was "in case we need another season" of a system.
wotlk ended with wrathful
cata ended with cataclysmic
and mop will end with prideful.Why prideful ? We don't have a real villain in mop and the story is more about control over emotions.We killed Sha of Pride and fight against Garrosh's arrogance.
If they had to end this season early, they had another one in store for us. We might not have another season after this.