Give me one good reason I shouldn't be able to have a customizable PC in Tetris.

Seriously: I think narratives in games should be based on player choice. To me, that's the difference between a game and a book or movie. To choose your own path instead of passively following one.

But clearly I am a minority here. Some of the biggest games are linear set-piece things with no choice in the narrative structure. Even open-world games tend to be linear narratively.

To use your example of Spec Ops: The Line: there is significant player choice that the main dude did not have to be a rigid character. They could have been as customizable as V from Cyberpunk 2077, and the effect would still land.