The mother of all poses in sex. This is where most people start and this is what's always there to save the day if everything else fails. Plus it allows kissing, biting all sorts of places within reaching distance, and so on. You cannot blame missionary to stick around, this is how men and women were made to have sex the easiest way. Just get those legs lifted up and penetrate that juicy thick creamy pussy like you have no other chance to do so later. You'll find this from time to time in every scene.