Why? Because Raptors are expensive!
China Tests New CZ-5 Rocket
Long March 5 is a Chinese next-generation heavy lift launch system that is currently under development by China Academy of Launch Vehicle Technology (CALT). Currently, six CZ-5 vehicle configurations are planned for different missions, with a maximum payload capacity of 25,000 kg to LEO and 14,000 kg to GTO. The Long March 5 will have the second largest "carrying capacity factor" of any rocket after Boeing's Delta IV Heavy. The CZ-5 rocket is due to be first launched in 2014 from Wenchang Satellite Launch Center on Hainan island.