Alright, I’v seen some pretty interesting takes on this, so here are my thoughts!
God Usopp: This is only because his dream is to become a brave warrior of the sea, and in order to do that, he will have to find the courage to sacrifice himself for the greater good.
Luffy: Luffy’s lifespan has been narrowed several times by early use of gears (2, 4, and 5), and Magellan’s poison. There is also a possible theory that devilfruit users get very sick when approaching Laugh Tale. He even ate a poisonous fish! However, I think that law will use his “Immortality Surgery” and give Luffy immortality at the cost of his life.
Zoro: Admittedly, he’s a walking punching bag. He almost died in his battle against Mihawk, and almost died to Arlong. And of course, he also took on Luffy’s pain back in Thriller Bark (I believe), and died then. He was only still alive because he got lost! He also literally had to get carried by Sanji in Wano because of his injuries from fighting Kaido. And right after this, he literally fight king and enters the domain of death! Dude, I get that my favorite strawhat has insane endurance, but he eventually has to run out of that and die.
Sanji: Same reasons as Zoro, just has more time left.
