Some gamers love to compare.
Comparing scores, comparing achievements, comparing speedrun, comparing collection, or comparing trophies.
If their experiences are too unique and different, it will be hard to compare.
Some love to compare, but imagine bragging rights of pulling off incredible or unique actions and outcomes that make the game more unique to the player?
If it was all pre-determined actions and events, especially for achievements, then that means everyone with the achievement has already done it.
Because Fallout 3 and Skyrim also sell stories.
Without that the main character will be boring.
For now gamers love if the main character's having a story.
Kiryu is also one of the example.
This scene wouldn't feel satisfying without Kiryu and Kuze story and boss fight battle before :

I understand what you mean, it's just games like Fallout and Elder Scrolls encourage players to define their own characters and make their own decisions. To make the Vault Dweller, Lone Wanderer, Courier or Sole Survivor their own characters. That's why these protagonists do not have names, they're supposed to be customizable characters.
However, events and encounters are still pre-determined in these games. You can go off the beaten path, but the side-quests are still pre-determined. The fact the Lone Wandered had daddy issues or the Sole Survivor has baby issues just made them less flexible characters in order to set them on a pre-determined path. Thus everyone has slain the dragon and rescue the princess, everyone has made the hard choices, etc.
Yakuza games however, while (somewhat) open-world, are supposed to follow a story. Kiryu and Kuze story. It's supposed to be pre-determined. I'm not saying there’s nothing wrong with games like that because it's supposed to follow a story.
I'm just saying, Bethesda boasting how their open-world games allow players to experience their own story, it's sort of a half-truth. You can freely explore, but your choices fall into the purview of scripted events, quests and side-quests than anything truly of free-will.
It's probably why Minecraft is still one of the most popular games we had for the last 17 years. While everyone has crafted a diamond sword or slain the Enderdragon, it's how players get from start to finish that varies wildly and uniquely amongst players. Granted, some of the game's content is pre-programmed, such as
structures. But given structures and its contents may have random variations' means players will still have unique experiences and challenges to overcome that they may claim as their own accomplishment over finishing a pre-determined quest.
I have nothing against games with their own stories that players need to follow. I'm just saying I would like to play a game where I truly feel free and be my own-defined character, my own isekai or alt-life story that takes into account my free-will, no matter if I choose good, evil, chaotic or lawful. I've yet to play a game that does that, and I believe AI serving as a games' "dungeon master" and content generator would allow us close to that,