Yes we have one night stands and hooking up... it's just that dating is something else. If you go on an actual "date" with someone (dinner, movie, etc) then it's implicit that you are looking for a relationship. It might or might not work out with that person, but you're going to at least give it a try (i.e. not see anyone else for as long as you're dating).
If someone is single and not looking for a relationship, it's perfectly normal for them to hook up with people at parties and other social occasions, or even to have NSA sex with fvck buddies. It's just not "dating".