Fucking becomes more enjoyable when you start out with kissing, whether you are an actual participant or a viewer of a porn film. There is something about starting to slowly first, then proceed to the actual deed that is so erotic. A lot of people do not like, and even get turned off, by porn movies that start with the dick already inside an asshole, or already inside a mouth.
It is a great warm-up to what is soon to come. Even the most hardcore porn fans know the value of starting a sex movie with its two stars kissing first.