Britain was heavily in debt after winning world wide wars. Its colonies were more an expense than a financial gain. Britain was over extended. Exploiting their colonies seemed the way to financially pay large debts. The American colonies rebelled against the taxes, leading to the 1776 Revolution.
Religion played a role, as American colonialists had largely tried to escape from the Church of England, beginning withe the Pilgrims and Puritans. King George headed the Church of England, and he was seemingly mentally challenged as well.