Sho-gekijo developed in reaction to the established modern theater in Japan, shingeki, during the era of student protests in the 1960s. Referred to as the “Underground Theater Movement,” sho-gekijo performances were informal, taking place in tents, on the street, and in theaters after the final movie of the day. The movement sought to free itself of the mainstream social codes and focused on dreams and fantasies versus the realistic portrayal of daily life of other theatrical forms. It was popular with the general population because it was more entertaining than enlightening, and did not require a high level of education to be enjoyed.

Sources Cited:
Wikipedia
A Guide to the Japanese Stage