Death is broken, it isn't just affecting Azeroth and thats an obvious thing that you aren't putting out. Its not filler plot or any stupid reasoning like that at all. The Shadowlands is where the problem is and well the rift above Icecrown is kinda a big problem as in theory anything from the Maw can get to Azeroth(Well Most of everything). Anduin and co are kidnapped because they defied Sylvanas. And considering how we'd go into the "Bad place" to rescue them. And no we aren't really going after Sylvanas to bring her back. People want her dead not "Bring her back."Would that shock you? This entire expansion has been one long extended bit of filler plot. Our reason for going to the Shadowlands are flimsy at best. We don't even come here to save all of creation, we literally come here to save Anduin and Pals, as well as dragging Sylvanas back to the denizens of Azeroth can take it in turns to smack her across the face.
Are you just ignoring the game to make your complaint sound logical? Cause you are pretty much ignoring Sylvanas's motivations and well what Zovaal wants. He's behind the BFA war and all those that were killed are now in the Maw which isn't supposed to happen. All of this isn't flimsy reasons to go to the Shadowlands. Zovaal even tells his plan "Death comes for the soul of your world." We know what that means. He wants Azeroth's soul for some plan to basically enslave reality to his will(He did create the Lich King so goal is the same).Now this plot isnt entirely without merit, the idea that we think we are doing something simple and it ends up being more complicated than we could ever imagine is a storytelling device that can work brilliantly. But Blizzard never seemed to figure that we need a reason to care beyond the baseline level of "kill the evil dude".
Shadowlands has essentially spent a full 2 major patches now mostly dragging its feet on why we should care to defeat Zovaal. The best the game can offer at this point is that we should defeat him because he is evil, not because he has really done anything do us or Azeroth personally to deserve it.
You don't just ignore a threatening thing like that and well we still had to rescue Thrall, Anduin, Jaina and Baine. There's more then enough reason to go to the Shadowlands. Even after you rescue our azerothian leaders we still have to be there because well leaving the Shadowlands would just leave us vulnerable to the Maw's forces. Sure we could ignore it but thats like ignoring the Burning Legion invasion via the tomb of Sargeras and we didn't ignore that. Zovaal may be evil(And thats a reason to go after him but even Bolvar points out he is the one who is the master of the Helm of Domination.
It all leads to Zovaal, the game even tells you why. He misleads Sylvanas about saving the Shadowlands but that was a lie. There's no dragging of feet. Just because we aren't on Azeroth doesn't mean the threat to it is fake. This idea that we have to be on Azeroth for a threat to her(the planet and world soul) be relevant or "important."