Think of a competition that you would consider entering. Think of one you would NOT consider entering. Lots of mathematics teachers believe that competition motivates their students. Their classrooms are highly competitive environments. Everyone works alone.
Successful students work for good grades.
Less successful students may make other choices. They may choose not to try because it is less painful to not succeed when you can tell yourself that you didn't even try. With others it may be a cultural difference. Females, in general, are not expected to be as competitive as males. That, of course, does not mean that there are no females that are highly competitive.