I wouldn't say most are, but as previously mentioned, late departure times to Asia ex USA allow for connections in Asia. Flights to Europe can leave as early as noon from the west coast and usually around 6pm-11pm from the east cost. You even have some early am east coast departures from places like BOS and JFK.
In cities without curfew it's worse. At DXB you can have 3am departures to cities in India.
Cheers,