The US was bankrupt. The army might have done OK on defence but it had not performed on the offensive. The Canadaians had shown they were not interested in all at joining the US. Canada was nmot defencelss. There was no prospect of further gains and lack of money was hurting.The question is why US ratified Treaty of Ghent ? Or stick to treaty after ratification. For US (back then) Britain was the hereditary enemy from Revolutionary War , they were incensed fall of Wahington and burning of White House , they had won Battle of New Orleans , they had much more disiciplined and regular army in 1814 instead of militia of 1812 and most importantly British army was being recalled from North America to Europe to deal with Napoleon's return and grab of power in France in 1815. For everyone it seemed like there would be another long Coalition Campaign against Napoleon in Europe in 1815 spring and summer (of couse Waterloo Campaign lasted only for five days) where British Army would play a more prominent role. So Canada was defenceless and up for grabbing. It would be very easy for US goverment to say "well since Treaty of Ghent did not satisfy our every national demand we want further concessions or else , oh look it would shame if we invade Canada since most of His Majesty's Army is busy elsewhere"