This is an important question, as considerations of audience dictated choices Stowe made in writing her novel that have been criticized in recent years.
Stowe's audience was middle-class white people in the United States. Her book is a polemic, written as an attack on slavery with the intention of persuading white people to abolish the institution. It was not written to Black people, as most were kept illiterate and enslaved in the United States prior to 1863. It was written to the people who had the political power to end slavery if they wanted to.
Stowe, therefore, creates a central Black character meant to appeal to white sensibilities of the time. She wanted to make Uncle Tom a person whites would wholly accept and identify with. For example, he works hard and obeys his masters as long as they don't ask him to violate his conscience. He is a good Christian. While he is grieved by slavery, he has no innate hatred or ill will toward whites. While Uncle Tom is a strong person who makes moral decisions based on caring for others, his depiction (especially as distorted in later stage and film versions of the novel) has sometimes led to revulsion in modern audiences, as he has come to be seen as too willing to kowtow to whites.
The novel has also been criticized as too sentimental, especially when it comes to the angelic child Eva, but Stowe's nineteenth-century audience loved sentiment. Appealing to people's emotions was widely understood as a way to change their behavior at the time, which was Stowe's chief goal.