Why did Jan van Riebeeck build a hospital?

He build a hospital because the Cape of Good Hope was a revictualling station for Dutch East India Company ships on their route to Batavia. Many sailors suffered from nutritional deficiency diseases, especially from scurvy, and had to recuperate at the Cape. Supplying fresh food and vegetables/fruit cured scurvy by supplying Vitamin C, which was absent from the usual ship's rations at the time.