Me and a friend of mine were having a phone conversation, and an interesting subject came up. Why do certain man go after a girl and does everything to finally get the chance to have sex with that girl?

Either if its dating  for couple of month, taking the girl out to dinner, movie or traveling long distance to see the girl.  But when the time come to have sex you go as far as making out, touching feeling sucking etc… and when its time to penetrate you back down and than give the girl some excuse like..”It’s not you its me”, or “I really want to make love to you but something is telling me no”, or “what happens after if we go through with this”….I don’t get it whats the point of all the work to get there in the first place.
Please keep it clean.