The Seven Years War is the solution (known as the French and Indian War in the US). In order to defeat the French and their allies from the First Nations, Great Britain had to spend an enormous sum of money. The colonists were thought to have struggled throughout the war but had greatly profited economically by the elimination of the French and Indian menace, according to Britain. The colonists believed that because they were the ones hurting and dying in the filthy little battles in the woodlands, they had already paid the price. Britain saw that it was the regulars that seized the Plains of Abraham and assaulted Louisbourg. The colonists were aware that their men, women, and children were being killed on their small farms. It was determined that the colonists would have to pay for at least some of their own safety because they had gained so greatly from the battle. The colonists believed they were making enough sacrifices for safety already without adding taxes. A sacrifice has to be made.
Another way of answering this:
Because managing colonies takes MONEY, which, as you must realize, does not grow on trees, as well as deploying and keeping troops halfway around the world to defend them from other empires who would want to get their sticky claws on them. You wouldn't expect the government to tax its residents twice to pay for the same advantages for the colonies, ensuring that they received nothing for free, would you? After all, they were taxed to pay for the administration and defense of the United Kingdom.
