There are many reasons that slave owners may have discouraged their slaves from creative expression, but the most prevalent reason behind it would most likely be the possibility of sparking a revolt. When people are given time to express themselves, especially when in an oppressed role like those in slavery, it provides one with the opportunity to plan revolts or planning to escape. When allowed to be creative, you mind wanders. If one was stuck in slavery and was then given the freedom to think and be creative, they would begin to realize exactly how bad their situation is, therefor sparking revolt:) hope this helps!