Why did the british loyalist flee the american colonies

Because they were loyal to Britain, so by fleeing from the american colonies they showed there loyalty. 

Loyalists were American colonists who remained loyal to the British Crown during the American Revolutionary War. At the time they were often called Tories, Royalists, or King's Men. ... Many outspoken or militarily active loyalists were forced to flee, especially to their stronghold of New York City.