unsystematisability of chance encounters
Places that become renowned as (or designed from the beginning as) facilitators of chance encounters gradually lose their functionality. They get overcrowded by people who come there to meet new people. These networkers destroy the spontaneity element completely and replace chance encounters with plain encounters.
You want to experience beautiful and organic chance encounters? Just wonder around the city and keep your antennas open. Other wonderers with similar instincts and interests will inevitably cross your path.