Believe it or not, by helping them you are doing yourself a favor. First of all , if you tutor them or help them out with their problems then you gain better understanding of the material than if you just studied it alone. Second, by helping them you are making them better, and if you are truly a competitive person like you say, then this should be a good thing because it should motivate you to be even better. Think about it, which is more of an accomplishment; being better than a C student or being better than an A student?
It could also be that you are just experiencing laziness and you don't actually want to do any work
