Also there is no "no sanding Army" requirement. There is only a requirement that the army can only be funded for 2 years ahead, presumably to require ongoing consent from Legislature, to prevent a Chancellor Hitler-type situation or a President becoming King by getting a huge multi year funding and then turning against the future Legislature and the country.
And the War of 1812 taught President Madison the danger of being under militarized and over-reliant on militias.
Many Founders believed a standing army to be an inherently corrupting force (if you have a warrior class, sooner or later they will make you go to war) and thought America would be better without one. Whether or not that could have been true in the abstract became irrelevant because the need to perpetually defend territory meant that there was never an opportunity to disband the Continental Army.