a town square isn't just a place, it's always a polity that requires common values and a shared culture. Otherwise you at best have an airport lobby.

A town square in Cologne where 90% of participants don't hail from Cologne but London, Mumbai and San Francisco aren't going to solve the problems of Cologne or have any stake in doing so.

Which also reveals of course what Twitter actually is, an entropy machine designed to generate profit that in fact benefits from disorder, not a means of real world problem solving, the ostensible point of meaningful communication.