Gotham's gala parties are famous, both for the wealth they showcase and because something almost always ends up happening at one. Anyone would say they should stop having the parties when there's a good chance a villain will show up.

In fact you're at one right now. The room is richly decorated, there are tables with food, waiters passing by with trays full of cups of drinks....

And Gotham's richest and most famous people are milling around, there are the members of the Wayne family, etc.