What was behind the growth of American resistance to British colonial policy?

Part of the reason that Americans protested Britain's colonial policy was the way in which the British interfered with American trade. For many decades, Britain had followed a policy of "salutary neglect," which meant that Britain did not enforce its regulations regarding trade. Their reasoning was that by not enforcing these laws, they would allow colonial trade and manufacturing to succeed (see the source below).
However, after the Seven Years' War ended in 1763, the British began reinforcing trade laws because the crown was in heavy debt from the war. As Britain had defended its American colonies from the French and their Native American allies during the war, Britain reasoned that the American colonists should help pay off this debt. To this end, the crown began passing new laws, such as the Stamp Act, which the colonists abhorred. Other British laws interfered with the trade that the colonies had already developed. Therefore, the interruption of American trade was one of the reasons that the colonists' resistance to the British crown began to grow in the years before the American Revolution.
https://historyofmassachusetts.org/what-was-the-british-policy-of-salutary-neglect/