That's because most women can only have a clitoral orgasm. The other type is a vaginal orgasm.
The difference is is that women who can only have a clitoral orgasm is because the labia do not cover over the clitoris. Therefore the clitoris does not get proper stimulation from just sex and must be otherwise manually stimulated.
In a vaginal orgasm, the labia do cover the clitoris so that when a man and a women are having sex, the sliding in and out of the penis causes the labia to move and the friction can stimulate the clitoris into orgasm. I have vaginal orgasms.