This is far from rare, especially at the high school level. First of all, it falls on coaches to design a program and practice structure that challenges and motivates the kids. However, this is obviously easier said than done, especially with the limited amount of time and coaching help that's present at most high schools.
So when it's not coming from the program, it must come from the player. This is a good lesson for players at every level though, and should be viewed as a learning opportunity. A player must be able to find motivation and inspiration from within himself to succeed.
If you rely on teammates, parents, fans, coaches...you'll be inconsistent at best. Great players do not ride the tide of the situation, they stay consistently high level all the time. They cannot be distracted by other's shortcomings because they are competing against themselves. Testing themselves and measuring their performance against their last time out.
Sounds good, but it can be hard. It's a real key to being a high level player, so you should expect it to be hard, and you should expect to have to dedicate a serious effort to it in order to get better at it.
One of the best things you can do is to set goals. Write them down and keep them to yourself. Even if your team has goals or your coach has some goals, keep some that are just for you. Small ones, big ones, extremely tough and not so tough. Keep a good mixture so that you can always be challenged to beat your last personal best but also you're not stuck reaching for something that's unrealistic. Constant accomplishment, confidence, and getting better.
Honestly if getting better at baseball and taking concrete steps to improve yourself don't motivate you on the field, you probably don't have a long future in the game as a player anyway. However this can be learned, and it can be developed.
Learn to test yourself, and if you get good at it, you may up inspiring yourself. Once you can do that, you're in good shape whether you're practicing or playing in a game.