Why did Maharaj make Kashiram's business fail and then tell him to feed ants sugar to teach him a lesson about pride?

While Maharaj did teach Kashiram a lesson about pride, the events occurred differently from how you've described them. According to Chapter 0, Maharaj's lesson was related to Kashiram's pride in giving Dakshina. Maharaj started demanding so much Dakshina that Kashiram eventually ran out of money and had to borrow, which humbled him. Once the lesson was learned, his financial condition improved. The advice to feed sugar to ants was a separate instruction given not by Maharaj, but by another saint named Janakidas Baba, which Kashiram followed faithfully.