It is clear from the very beginning of the novel that Baba is disappointed about lots of things that he sees in his son, Amir, his penchant for writing being only one of them. Consider how Chapter 3 ends - Baba, talking to Rahim Khan, says that Amir is so different from him that he doubts he is his son.
An interesting part of the novel that is worth examining comes when Amir writes his first story and gives it to Baba, saying that he had written a story:
Baba nodded and gave a thin smile that conveyed little more than feigned interest. "Well, that's very good, isn't it?" he said. Then nothing more. He just looked at me through the cloud of smoke.
I probably stood there for under a minute, but, to this day, it was one of the longest minutes of my life. Seconds plodded by, each separated from the next by an eternity. Air grew heavy, dam, almost solid. I was breathing bricks. Baba went on staring me down, and didn't offer to read.
It is clear that Baba has no interest at all in his son's literary ambitions, and it is left to Rahim Khan to encourage Amir and read the story. If it were up to Baba, Amir would be a businessman or something more "manly" - a writer does not fit Baba's idea of a male career.