We gather because meeting IRL is much different than a virtual meeting. There is much more out-of-band communication, more opportunity to let the discussion meander naturally, more space and time for serendipity. It also encourages small groups and in depth discourse without a predetermined end time. Virtual meetings tend to favour the opposite, such as one-to-many communication.
Gatherings also permit groups to discuss during a low key activity, traditionally chores, but could be anything informal and not mentally demanding, like a stroll or a meal or playing cards.
Gatherings can be structured to play to these strengths. I think the Shenzhen gathering did better in this regard, than the Panama one, which was more agenda focused.