Structure is useful; there's a social burden to going out of your way to arrange a one-on-one hangout. I wouldn't bother to do that with someone I'm not already close to, but I'm loving this structured arrangement where I don't have to feel awkward about reaching out myself.
Ok, but again, there is nothing stopping people from doing this as a group. There is no "magical" structure that comes from a work meeting. A group of people at work can decide to organize something on there own. You are talking about one-on-one stuff, which is different.
I've had plenty of extremely productive outcomes that started as a serendipitous a conversation in the break room with someone who is not in my day-to-day (or weekly) orbit.
Different stuff works for different people