Some have already been stated by others but I too suffer from reload syndrome in shooters. I only play games once also, don't have time to be playing it over again and to me once the story has completed the game is done. My interest is gone cause I already know how everything ends and the big interesting moments. If the game has more than one ending , I will just youtube the other endings, I'm not devoting another 40+ hours of my time for the same experience and 3 minute of an alternate ending.
I have to complete side missions before main story. If I beat main story side missions are meaningless to me and will never get finished.
If it's a game that is action/adventure or horror that allows you to have somebody join you from online in the campaign (ex. resident evil 6) I never use the feature. I will play campaigns strictly offline with computer AI. I will try online once just to say I did it but , but randoms online annoy me. They either don't have mic's so we can't communicate well, or they run around doing dumb sh1t, or they will take away from exploration by rushing through scenes, scenarios , or telling you where everything is without you trying to figure it out.