Because you've spent the last 3-4 books reading about this guy and his long journey through life, the desert and everything in between and getting to the promised land is the overarching goal and then he gets there (if you look at a map the mountaintop on which he dies is in the promised land, but only on the outskirts and its not the best in terms of resources) and bloody dies. Its like walking from Mongolia to get to Buckingham Palace with 50000 people in tow and getting there but then dying on the doorstep. Like, you all risked everything for this. This was your life. And then you just die.
And he's pretty chill with it (???). And its premeditated for legit no reason. And it's so frustrating.
Doesn't exactly help I view the whole story as a metaphor for our journey through life and its like... Does anyone get there? Really? Urgh, it bugs me writing this.