That's cause this duty is only needed for this progression in the MSQ and part of an Roulette, with like 20 others.
Just as a sidenote and tip, if you try to do this story duties, make a party finder group and say you are doing it for the first time for story progression. so you will find people faster than normal queueing.
But to say it now, after this you have like 110 more main story quests to do before you will reach the Heavensward areas and its content.