Ok, this is an absolutely fair question and the answer is that nobody in real life kisses like people in fanfic. Nobody “plunders their lover’s mouth”. Tongues do not “battle for dominance”. Two people kissing do not look like they’re trying to “eat each other alive”. I can’t explain to you exactly why fanfic (and writing generally for that matter) is so bad at describing kisses but if I had to guess, I’d say it’s that it’s difficult to make actual kissing as it is practiced by normal, non-slobbery human beings sound exciting:
“A’s mouth pressed against B’s gently, then more firmly. Their lips slid against each other as they both tilted their heads, slightly varying the pressure. B’s tongue made a brief appearance to brush against A’s lower lip, then receded. They parted momentarily, then pressed their lips together again, firm, then gentle. They continued in this vein until a) they had to stop because you can’t actually take off your clothes while your face is attached to someone else’s, b) they got bored, or c) they misjudged the angles and knocked their teeth together, which is a thing that never happens in fanfic, does absolutely happen in real life, and really fucking hurts.”
See what I mean?