I wouldn't focus too much on it. Just so many activities that rely on people feeling comfortable, in a familiar, intimate atmosphere. You can't spoof that with a restaurant or an AirBNB. So even if the place would allow it, people would rarely be as comfortable.

Oh ok, I'm one of those people who do have such parties lol (though I'm normally the suspendee).

Funnily enough I have had parties outside with such aspects, there are actually venues that specialise in such things. Friends regular rent them out. Usually combined with finger food only though.