The main reason as to why the main attraction is Primals. ( Spoilers)

[Starlord]

Story.

It revolves around the story more than anything else. If I recall the Ascians are looking to summon all the primals ( in their ultimate state) in order to drain the Mothercrystal (Hydaelyn). In which your Character has a vision seeing the Mothercrystal ( Hydaelyn) drain from it's light and we see nothing but a darkness crystal.

The Ascians main motive in all this is so they can summon Zodiark their "God". So they taught the beast tribes on how to summon primals, the more the beast tribes summon their Primal the more Hydaelyn's light fades until it turns into darkness. Which is probably their cue to summon Zodiark ( somehow) while Hydaelyn is in darkness.

A Quote from Lahabrea: “The end of your tale is but the beginning of another. The tale of the Crystal's demise.”

How is the Crystal going to be in demise? Primals draining the energy from the Crystal eventually turning it to darkness.

I understand people are complaining about All they do is Primals. Well this is the main reason why they can't simply drop it.