Of course many parents place emphasis on winning for the following reasons:
1.) They are living vicariously through their children
2.) They want the child to go pro / be famous and make them rich
3.) They have nothing else to define them other than my child is good at _______
I think often many parents often become too invested in their child's teams performance and forget that it's just a game, I think this can lead to conflict and issues about something that really shouldn't be a big deal, I think that people just need to remember that it's all supposed to be about fun while still trying hard.
Often enough, a child athlete will not win. There are just not enough spaces for winners. However, stressing winning and losing will support a behavior that adapts to society later on. If a child loses at baseball, perhaps they would be successful at soccer, or chess. The winning and losing aspect of competition doesn't need to be zero-sum. It can be beneficial to the loser by motivating harder practice, or choice of a different activity that they are more proficient at.
Athletics can be fun, fitness-oriented social outlets, but ultimately, the point of any athletic pursuit is getting on the field of play and competing and winning. So, no, parents can not put too much focus on winning. Winning is the entire point of athletics. Tying their child's self-worth to winning is too much, but that's not focusing on winning.