Bonkers, currently exchanges are only open from 9:30am to 4pm EST Mon-Fri. So your "doomsday" argument is equally applicable - most companies make announcements outside trading hours and most unhedged investor loose money once marker opens if announcement is negative.
Typical US equity trading hours roughly coincide with normal working hours. Not many people would want to stay around too late. Even if they did, the liquidity they need may not be there because most people have stopped working for the day.
