Why does Rasheed continue to taunt mariam when he has absoulute control over her?

The direct answer to this is that Rasheed is simply a bad person. Rasheed is a hulking man. He is also an abusive jerk and a first class misogynist. Rasheed tells Mariam that she needs to start acting like a wife and stop crying all the time. Mariam begins to clean, cook, and shop for food. One day Rasheed comes home and compliments her daal, Mariam feels proud. Then, Rasheed tells Mariam that "a woman's face is her husband's business only" and gives her a burqa to wear, which horrifies Mariam. We can begin to see Rasheed's passive aggressive patterns of emotional abuse beginning already.