For me it already starts quite early in open world games, long before the post-game content. I narrowed down the issue, at least for me, to the open world concept.
Nowadays we have gorgeous looking, ridiculous large open worlds, with the pretend of endless possibilities. Yet, we are put on rails, forcing us to travel along the predefined path, just like linear games, where we proceed through small separated maps without any way to go back. Non-open world games are even more satisfying to finish, because we know, we can't go back.
But open world games seem to mock us, by giving us access to huge worlds, but offer only the predefined path, guiding us through the story. Well, here is the twist. Putting us on rails so that we experience the main story in the right order, is by no means a bad thing.
No, the actually bad thing is, that the rest of the vast open world around the story is right there, just a few steps off the rail, seemingly unused due to just little things we can do with it, before we return onto the predefined rail. And the few things we can do, usually turn out to be tedious things, like collectibles or monotonous side quests. The open world is reduced to nothing more then a giant set piece, that we're mostly not supposed to interact with, just there as a beautiful background and the illusion of freedom. It's like: "Hey, here is a really big world, where you can go anywhere you want, free to explore every nook and cranny! Meaningful gameplay apart from main story and side stories not included...
It makes me sad, to see that the open world concept never seems to be developed further, allowing us to interact with the game world in meaningful ways, be it alongside the big main story, or post-game. I am going to end my, let's say moderate rant, with a question...
...why creating a vast open world, that swallows countless of hours, work and money to create, when there is barely any gameplay to interact with it, that could justifies the existence of said open world?