Why did congress refrain from including the power to tax in the articles of confederation

Because It could raise money only by borrowing and by asking the States for funds. 
Back then, the government already drowned with massive amount of debts due to the expenses that we made during the revolution and the abilty to ask states for funds would hindrance the economic growth in states level.

This would be a true statement

This would be a example of a "i want to be single person"