Because of different time in the world, people are constantly using the internet non stop. Even do it is night time in China, if the time in Russia is day time, then people are still using the internet. Like in the market, because of people constantly accessing the market, it will never sleep and rest. The only time it will take a rest if the all the users are no longer active.
What you said is correct market runs 24 hrs and it is due to different time zone each country having and due to it trading is going on 24 hrs.