Why do some historians argue that slavery in New York was even more restrictive than in southern colonies

The systematic enslavement of African people in the United States began in New York as part of the Dutch slave trade. The Dutch West India Company imported eleven African slaves to New Amsterdam in 1626, with the first slave auction held in New Amsterdam in 1655.[1] With the second-highest proportion of any city in the colonies (after Charleston, South Carolina), more than 42% of New York City households held slaves by 1703, often as domestic servants and laborers.[2] Others worked as artisans or in shipping and various trades in the city. Slaves were also used in farming on Long Island and in the Hudson Valley, as well as the Mohawk Valley region

During the American Revolutionary War, the British troops occupied New York City in 1776. The Crown promised freedom to slaves who left rebel masters, and thousands moved to the city for refuge with the British. By 1780, 10,000 black people lived in New York. Many were slaves who had escaped from their slaveholders in both northern and southern colonies. After the war, the British evacuated about 3,000 slaves from New York, taking most of them to resettle as free people in Nova Scotia, where they are known as Black Loyalists.

Of the northern states, New York was next to last in abolishing slavery. (In New Jersey, mandatory, unpaid "apprenticeships" did not end until the Thirteenth Amendment ended slavery, in 1865.)[3]:44

After the American Revolution, the New York Manumission Society was founded in 1785 to work for the abolition of slavery and to aid free blacks. The state passed a 1799 law for gradual abolition, a law which freed no living slave. After that date, children born to slave mothers were required to work for the mother's master as indentured servants until age 28 (men) and 25 (women). The last slaves were freed on July 4, 1827 (28 years after 1799).[1] Blacks celebrated with a parade.