And with these highly realistic elements

comes more complex gameplay, and complex gameplay takes a long time to get up to speed
These details also require more play time. This is why a game of ZERO HOUR must take longer than R6, which may seem like more fun the longer it is played, but it is not.

If it's an FPS with large maps and large battlefields with many players
Battlefield, Call of Duty: Warzone etc., the game length does not affect the gameplay too much, but for CQB games the game time is also an important factor in the gameplay.