Because scientists are HUMAN BEINGS just like YOU are. We have all the hormones, instincts and emotions YOU have, including the instincts to REPRODUCE, SURVIVE and teach people to preserve societies, tribes, extended families, cultures, traditions AND civilizations. Insane people like YOU seem to think it is requirement for all scientists yo repress and suppress all instincts and emotions. That does not happen the real world. Yes, some scientists are single and celibate, or almost celibate, That may be by choice, or it may NOT be. It is not something we have total control over.