Wow is a pretty large story and this is only a beginning from a beginning. It is also many stories and many books long with a complex Lore which is based on our lores of mans’ past placed in fantasies . As I said in above ,
Not every story suites everyone desire.
Being the current writing room on a Saturday, just about breakfast.
This is my problem with the entire SL story. We have no idea why the Jailer is “bad”
The Jailer: “I don’t want power! I just want everyone to serve me…”
Honestly, the whole thing is dumb. Why is he “the Jailer”? He was supposed to be a prisoner. Just because “jail” and “prison” are synonyms doesn’t mean “jailer” and “prisoner” are, Blizzard. And why even have the Maw? If things can be killed in the Shadowlands, why make a place where you send all the souls that would willingly follow Zovaal and leave him there, unguarded, so he can build up his forces in safety? It makes no sense to me.
Ugh, I need to stop thinking about the story. The more I do, the angrier I get. And it’s not worth getting angry over anymore. It should be forgotten at this point.
I mean, that is his goal. He says it quite clearly in the cinematic at the end of Sanctum of Domination.
“Too long I endured the Maker’s flawed design. I will forge a new reality where all will serve me.”
So clearly he’s intending to go into Zereth Mortis and use the tools in the Sepulchre to remake reality to the point where all beings serve him.
Because he can’t make them himself, only the Covenant Leaders can make sigils, and they’re obviously not going to give theirs to him willingly (with the exception of Denathrius’s sigil). Remaking new sigils is also not easy, it required quite a bit of work to create each one. We just managed to complete the quests in a few hours, because I seriously doubt people would tolerate a week long quest chain to create each sigil or something like that.
The sigils are the keys to the lock that kept the portal to Zereth Mortis closed. Without them, no portal.
No, they don’t, because those other infinite afterlives are not governed by the Pantheon of Death. There are an infinite number of Afterlives, we only get to visit the ones that are governed by the Pantheon.
Well he kidnapped and tortured our heroes. So he clearly is bad. 
I think he’s trying to break the cosmic cycle. Whatever that means tho…
Exactly this. We have no answers and they (Blizzard) have no clue.
This is the only way to extinguish this dumpster fire, at this point. It was all just a fever dream.
All ice cream will be vanilla but it’ll be the most bland flavor possible.
To address this small part, IMO as the Jailer was concocting his grand plans, much of it rested on the fractured nature of the Shadowlands. The vaunted Maw Walker helping out to unite and change things let to the cooperative effort that was able to forge new sigils.
Which is funny cause, I recall the Primus and Eternal ones saying they stopped Zovaal from getting the sigils before, so unless like the First Ones took the Eternal Ones to Zereth Mortis and showed them how to use the machine… Zovaal shouldn’t be as clueless about how it works as we are initially…?
I think the only thing that’s clear with this dumpster fire is;
“It makes sense when you don’t think about it! We certainly didn’t!” -Steve Danuser, Narrative Lead; World of Warcraft.
N’zoth bad dream would be the Best Case Scenario 
I don’t known since it’s cycles the only way to do that is to stop time ,dissolve everything if it were in our reality but it’s not it’s in sl reality.
Not true. Sargeras was a good guy until he saw the nature and damage of the void, and he tried to fight it, but went crazy knowing it was a futile and endless battle. The burning legion was created to destroy the universe so it wouldn’t fall to the void
Sargeras has more motivation than the jailer.
The only thing that has been hinted at in passing is that his remade reality would involve breaking the cycle that is life and death. As to how said cycle works exactly 
We see souls from the realm of the living in the Maw and the domains of the covenants. What exactly from the afterlife is cycling back in to life? With what we see in the different domains and how people are just kind of reborn in the Shadowlands it begs the questions of Who, What, and How are souls flowing back out of the Shadowlands to make life anew as the story implies. NON of that is addressed while a painful amount of time is spend examining what happens to souls that enter the Shadowlands.
As for the Jailer we also had been told towards the start of the Shadowlands that The Jailer wanted Azeroth’s Titan World Soul just like the Void. I assume that is another thing they are going to elude to when setting up this “grand” conclusion.
A few weeks back I was talking with someone with questions about how the Shadowlands works and going in to detail on that post and trying to answer this person with concrete established lore was actually fairly difficulty given how loosely blizzard have been structuring the rules that make up the Warcraft universe.
The Shadowlands is described as “the realm beyond realms” Then we have dimensions within realms and or plains of existence which run paralleled to the world within realms. Meanwhile they are all connected and despite some being mortal or immortal realms people of ether persuasion can go from one to another removing any sense of distinction between the two. Some realms exist within the same space other within different spaces meaning its more like they are in different dimensions… I am sorry there cosmic lore just sucks at this point. At least in other universes like Star Wars the ground rules are very clear and kept consistent thought there franchise.
WoW is at its best when there story telling focuses on Character interactions. Seeing our favorite characters be apart of this world. A big part of that is them eventually passing and letting other new promising characters take the spot light. Andin has been the focal point of most of these interactions since Legion and he has been grossly miss handled by being sidelined again and again. In addition we have several really good characters that debut in BFA but have also been left behind for forgotten because OH LOOOOOOOOK ITS THRALLLLLLL 
there was some real potential to have climactic moment with these overused characters and bring some closure to there burnt out character arcs by using the afterlife as a device to have confrontation LITERAL confrontation with there demons with us at there sides. Instead Thrall was 2 levels below us when we found Garrosh. A large number of these characters are played out beyond belief.
So if Blizzard has no idea how to finally get some closure to the Thrall and Garrosh conflict how they hell are they supposed to write a grand cosmic war that is interconnected across 15+ years. The reason for this is because: The game can’t end.
What is the Jailer trying to do you ask? Nothing, he is doing nothing at all because there is no end and there are barely any resolutions. This is Warcraft writing in the modern era. They write so they can keep writing.
Maybe Zovaal is a narcissist, he didn’t build the machine of death the way he wanted so he’s all spoiled kid on us and just wants to break it all so he can build it his way. wah wah wah
Something, something bad guy something evil.
Does any bad guy need a purpose to be bad?
Jailer: “It’s all a lie!”
Everyone: “What was the lie?”
Jailer: “All of it!” 
I wonder what type of flaw a mad man see?