Actions tend to bring us up because we can DO something about it. So, try to talk with him in ways that encourage actions in the future and give up trying to figure out how he got this way in the first place. It doesn't really matter much why he is the way he is. Men need to be able to take actions to solve problems. They are not like women.
Women tend to want to talk to solve problems.
Talking about problems can bring a man down. He needs an action to take to solve his problems. You say he's good at fixing cars and things. To fix a car is to take action. Maybe you should try to figure out what actions he could take to build a better attitude.