Florences pull in people of multiple disciplines because A Florence is a city with multiple world-class scenes. People want to be part of the scene so they go to the city. (Geeks, Mops, and sociopaths in subculture evolution ) People will only go to the place if they know about the scene so this is true only at a certain point in the city’s evolution.
Hong Kong and Singapore are currently a place where world-class Finance people want to go but people of other disciplines are pretty meh on them.
Paris and Florence were places that pulled world class people in multiple disciplines. Florence pulled artists, inventors, merchants, writers. Paris pulled in artists, inventors, chefs.
A repeated pattern seems to be that Florences require a world-class high-profit discipline and a world-class cultural discipline