Both of those examples are lost on me; I've never done WoW and never watched Lost.
For the former:
The base game and the first two expansions dealt with foes from the strategy games, and were quite popular. But that meant that at the end of the second expansion, they had to write mostly new story. It was often amateurish writing at best, and it fell into a pattern...
BBEG X: "Hah! You thought you knew what you were facing. But those were just pawns in MY master plan!"
[The mortals squabble, but ultimately resolve their differences and unite against their common foe, mostly because it's an inarguable existential threat.]
BBEG X: "Fools! You know not what you've done. An even greater danger awaits you...that I tried to stop..." [they die.]
Mortal faction A: "Back to our regularly scheduled squabbling and war crimes?"
Mortal faction 1: "
Obviously, I'm surprised you need to ask."
Ally NPC of the week: "Oh no! We are disunited in the face of the greatest peril the realm has ever known! Disaster is about to strike!"
Disaster: [Strikes!]
Both mortal factions: "How could we
possibly have seen this coming when we were so focused on murdering the people we've allied with multiple times before!"
[Repeat from beginning.]
This cycle repeated something like four or five times. To the point that, by the time they hit the eighth expansion, Shadowlands, they had literally had multiple competing, contradictory "master planners" who were
all, somehow, pawns of the same (allegedly)
ultimate master planner...whose death simply passed the buck to something that was, somehow,
even worse than having a tyrant reformat all of existence into his personal playpen.
Or, in brief, every single time people defeated the big bad enemy, Blizzard would then say, "but wait! This was just a prelude to the REAL fight!" in order to keep people going. Constantly delaying the conclusion. Constantly stringing the players along, promising that the
real problem, the
real solution, was just around the bend, Tune In Next Time.
This honestly worked for maybe a decade, give or take. But Shadowlands (8th expansion) broke the spell. Players were fed up and left the game in
droves, because they finally got more sick of waiting for a real conclusion of
some kind than they were eager to see what the next danger would be.
Lost is a bit simpler by comparison. They acted like there was a grand mystery to solve, but there wasn't. The writers just put in weird things, mysterious things, symbolic things with no clear explanation, and let the rumor mill and over-eager fan theorizing foot the bill. This escalated with every single season, adding new layers, new contradictions, new unexplained symbolism or the like. By the time they reached the sixth and final season, and thus had to pay the piper...it was too late. They had far too many mysteries and zero answers. Since the mystery was the compelling element for many fans, botching those answers or (more commonly)
never giving an answer at all was...unpopular to say the least. I have heard that folks binge-watching it today have a better response because they don't have time to get strung along, but even they admit that multiple parts of the grand finale are disappointing at best.
In both cases, a necessary conclusion is deferred far, far too long, and that means that even if a decent conclusion
does eventually arrive, it's already gone sour.