What is a realistic medium? Realism is something that is natural or something that happens naturally.
Usually, realism is used to depict a subject matter truthfully or as it is without any artificial add-ons. In theatre this was usually meant to bring direct attention to social and psychological issues of daily life.
Sometimes theatre acts as a medium to transfer knowledge and a social message which is initially difficult to portray. For example in the movie Dear Zindagi where Alia has emotional issues, the movie was a main highlight to make people aware of the fact that psychological or emotional issues are there and they are not something to be taken as taboos and have to be addressed with care just as we do with physical problems.
Theatre has been the main source of educating the masses and brings a sense of social awareness. They were a major medium to convey messages, especially during the British period. At a time when all things were considered anti-nationalist it was through this medium they tried to make people aware of all the injustice done to them and asked them to fight.
Even today we see that theatre has been used in a similar manner to tell the macho man stories. Saving the damsel in distress and things like those that were abstract have gone and more of real essence has come in.
Even people prefer watching something they can relate to instead of some masala madness.
Movies like Mardaani have been used to bring attention to growing rape and child trafficking, Padman and Toilet: Ek Prem Katha was revolving majorly on social causes that were taboos. Also, some historical movies like Padmaavat and Tanhaji have tried to showcase some historical events in pictorial representation. These are a few of many movies that promote and are more realistic.