First of all let's start with stamina no one can play for 48 minutes in professional basketball today without losing performance even LeBron does not play that much, but here they do not lose abilities at all.
Nobody plays 48 minutes in professional basketball because they choose not to. Here you can make your players to play 48 minutes. It's as simple as that. Even in professional basketball, all the players could play 48 minutes, if the coach instructed them to do so, and the players have nothing against playing the whole game.
All of my players in my team have abilities at least more than mediocre but after the game when I see the Team Ratings and get more than awful I am amazed. How did my team achieve that?
Just because all your players have skills at or above mediocre, that doesn't mean that your team rating will all be higher than awful. It's not a direct proportion.
And the worst thing that happens and proved my point that this game sucks was this at the end of the second quarter the opposition's team player had 5 Fouls, but he still played 38 minutes and did he foul out ???? of course not !!!!!!!!!! is that even possible not to get fouled out at that situation?
in BB, players get fouled out when they have 6 personal fouls.
It looks like you have quite big room for improvement and understanding of this game. Also you need to think little more logically.