This is just the realism factor
VS. immersion.
The realism causes a problem as it actually removes the Immersive feeling when you're pulled out of a career. Yes,
Realistically speaking, during WWII Submarine Captains had an average of 3-4 patrols with sometime being extended to half a dozen or even 10; But this removes the immersive feeling when you're playing the game.
This is
The Thin Red Line between the two where they can oft hurt each other if the line is crossed.
Take the following for example: Yes, it's realistic that a captain would not have to produce the entire solution for the the torpedo, but the game lets you do that to increase the immersion and overall interaction with the game.