Since people everywhere (China in this case) were looking for a religion they could rely on for peace or whatever reason, Daoism was the religion they could go to.
Confucianism, despite some rulers disagreeing with the idea of some of Confucius' ideas, was not a religion, but it was like a philosophical thing for the Chinese. It was especially popular since they used it for meritocracy, or people selected to rule based on their knowledge.
Both became popular due to trade of ideas of both concepts on the Silk Road.
