Some women like it because oral stimulation is very sensual and can be very sexually arousing. They do it for themselves and their guy. They enjoy giving pleasure and seeing how much their guy enjoys it increases the woman's pleasure. The smooth texture of sensitive skin of the penis on the tongue, nose and lips is very sensual. The taste. The woman is in control. All five senses are activated and stimulated simultaneously. It's very bonding especially if there is some eye contact involved. These are just some reasons along with others that have been listed.