Why are Peking opera lyrics often written in colloquial language?

In the context of Chinese performing arts, jingxi (Peking opera) utilizes colloquial language in its lyrics primarily because it was designed to be widely patronized by local audiences.1

Emerging during the Qing dynasty, jingxi became a popular form of musical theatre that was frequently performed in public teahouses, which served as both rehearsal spaces and venues for regular performances. While some critics have noted that these colloquial lyrics may lack literary merit, the use of everyday language helped make the highly theatrical and vigorous performances accessible and engaging to the general public. This contrasts with older, more restrained forms of drama like kunqu, which were often more formal and elegant in their presentation.1