Judy Murray is a very pleasant person who has worked hard to give her son's a decent start in life, and to make the most of their natural abilities.
The fact that she has been thrown into the limelight purely because she has done this is incidental.
Neither did Andy seek fame (unlike many showbiz 'stars'), and he is passionate about his sport.
Why shouldn't he show disappointment when he knows he hasn't give of his best.
Believe it or not, to a true sportsperson, they do care when they lose---because they know they could have done better. They replay in their mind every shot they messed up, and when they win then euphoria takes over.
He has also physically suffered, as well as enduring years of hard slog, away from home and family, travelling many miles at home and abroad,around small tournaments, before he was even heard of.
However, don't start me on the so called sportspeople who play Premier football. Different kettle of fish altogether