The pleasure it can cause can encourage females to have sex.
The involvement of the human cervix in reproduction and sex.
A argues that the female orgasm may have no obvious evolutionary benefit and that it may be a relic of a time when the hormones associated with orgasm were necessary for a woman to ovulate.
This may also promote bonding with a sexual partner, which does have significant evolutionary benefits.
While vaginal orgasms are less common than those from clitoral stimulation, some women have them — with or without other stimulation.
Others may simply be uninterested.