Answer: Because of the things she did below. (Teaching, etc.)
This was in direct contradiction to the teachings of the Puritan faith, which stressed an avoidance of sin because it was thought to prevent admittance to heaven; as well, the Puritan leaders didn't appreciate having Anne or anyone else question their role in the church or in the wider society. One other irritant to Puritan authorities was the she, a woman, dared to teach men–for among those dozens who regularly attended her prayer meetings were both women and men–men in religious matters.
In 1637, Hutchinson was warned to cease and desist what the Puritan leaders said were heretical teachings; she refused. When she was called to a meeting with church leaders to explain herself, she refused to recant her teachings, refused to live by the directions set out by Puritan leaders, and said that she was following her own path in life because she had a direct connection to God. For all of those things, but especially for the last one, she was banished from the Massachusetts Bay Colony. She was allowed to stay through the winter, under house arrest. In March 1638, she and her family joined Roger Williams in the colony of Rhode Island. In a testimony to just how influential Hutchinson had become, 30 families went with her. They founded the settlement of Portsmouth.
