Why is this how the saves and misc stuff routed...

        I am not sure if this has been mentioned before, but I feel its important to know why the directory for mods, saves and all that other stuff has to go to documents in the main drive of any computer. I like to have extra content on my games to help create really good and immersive characters for when I play. But eventually my drive runs out of space and I am forced to delete mods.....
       Now yes there apparently a way around this by tricking your game into thinking its going into the main drive by some sort of linking using the command prompt for windows but that's such a complicated method and is unfair to those who can't do something like that or are not as tech savvy. And Sims is not the only game like this. I just can't come up with other examples since they're not games I have (I think...).
Anyway, I just find its really stupid honestly. It should be a choice. When I installed the game and was gven the choice of where the folder would end up, I was under the impression that it would include the previously mentioned folder.
         I have things I do, I am a photographer, especially with games. And those pictures pile up ya know? And I have games I want to run the fastest and put them on my main drive. I don't want to have to upgrade my main drive or buy a new SSD just so I can have the speed for a few games when speed isn't what I worry about with The Sims....