Shanks is generic trash and makes the story less interesting.
By ending the Marineford war, he ended the manga before more interesting plots could reach their climax.
So you might think I want him to disappear from the story,
But by being the only Yonko who we still know nothing about this far into the Yonko Saga, Shanks makes the world feel smaller and less interesting by his absence.
In other words:
Whether Shanks shows up in the manga to do something, or whether he is absent, his existence makes the manga worse and he should’ve been killed off a long time ago.