>>7128003027% of players completed Oblivion (released in 2006), a game with a 25 hours long story.
Reasons often cited for low completion all culminate in GTA6:
- open world is a distraction, the sandbox aspect means people just fuck around without ever progressing
- the longer the main story, the more people will drop as it makes the story lows and buildups last longer
- people don't have as much of an attention span as in 2006
Now imagine when every retard on the planet with a console or pc buys it because "it's le most expected generational impacting game :%))))". Sure it will sell a lot, because of player expectations, but when people realize what they paid $100 for, the following games will sell less and less. See already all the people that defend the game because it's a "great shooting/driving simulator". I don't think 5% of them will beat the game.
That's also why they don't make DLC that expands on the main story: because no one fucking plays it. Pokรฉmon does it, Xenoblade does it, because those are games where a significant amount of players play to the end. You don't make DLC that 90% of your players can't use even if you give it away for free.