Why do China people speak English abroad and foreigners come to China to speak English?

Because English is the universal language.

If foreigners come to China to speak Chinese, by the same token, you have to speak Japanese when you go to Japan, Spanish when you go to Latin America, Hebrew when you go to Israel, Thai when you go to Phuket, and Indonesian when you go to Bali ... Do you think this is realistic? And English is a great tool to communicate with local people, even if you don't know the local language. It's the same for those foreigners.