Only Lordaeron is scenario, rest are regular story quests.
Majority of players will be play, as the playerbase is overwhelmingly casual and incompetent, sticking only to basic in-game stuff. Forum posters are tiny minority.
Overall, its nothing new, every pre-expansion is like this. If the legion invasion didnt give xp no one would do them either after earning the achiev.
Tl;dr Looks like you are new to this game, people will do event and continue waiting for expansion, like they did 6 times already.