Why do trains from Beijing to Shanghai depart from Beijing South instead of Beijing Central?

The current Beijing South Railway Station is a large railway station on the south side of Beijing that opened on August 1, 2008. The new station replaced the old Beijing South Station, first known as the Majiapu Railway Station and later known as the Yongdingmen Railway Station before 1988, which stood 500 m away and operated from 1897 to 2006. The new Beijing South Station, is the second largest in Asia,after Shanghai Hongqiao Railway Station,and joins the Beijing Railway Station and the Beijing West Railway Station as the third major passenger rail hub in the Chinese capital. It serves as the terminus for high-speed trains to the city, including the Beijing–Tianjin Intercity Rail, which can reach speeds above 350 km/h. The Beijing South Station is served by Subway Line 4. It is also accessible by bus, including Routes 300 and 458, and taxi. It is situated about 7.5 km south of the city centre, between the 2nd and 3rd ring roads. Train from Beijing to Shanghai Schedule http://www.chtrak.com/result.php?from=beijing&to=shanghai