the more you touch someone the more they become accustomed and even expectant of being touched by you. It's one of the ways humans show attraction, those little gestures of arm over shoulder, gentle grazes on the leg, even just lingering your hand a second longer on their waist, that built up over time into "this is a person I trust enough to let touch me affectionately."
O'course, in real life if you walk up to a random stranger and poke them ten thousand times in the boobs, they don't miraculously fall in love with you. Unless... maybe I've been doing this dating thing wrong my entire life...
One sec, brb to let you guys know if I've got a thirty girlfriend harem or just need someone to post my bail.