Why were men of longer periods of enlistment preferred by Scott?

They would have more experience, which was important since they would be fighting in enemy territory.

It would take time to accomplish the tasks ahead of them.

Men with longer period of enlistment tended to do better than short-term enlistees, who were never far away from going home.

he War of 1812 sent the Army of the young republic a decidedly mixed message of valor and glory interspersed with cowardice and blunders. The performance of both regulars and militia had been very uneven, although each improved as the conflict drew to a close. In a sort of role reversal, what glory did appear from the victories on the Niagara frontier in 1814 had gone not to the fabled citizen-soldier but to the oft-despised professional. Admittedly, the militia, when properly led as during the Battle of New Orleans, had on occasion done well; but after the war many military realists questioned the ability of the Army to employ him effectively. There were several reasons for this. It was extremely hard to obtain from state governments accurate figures on how many militiamen were available. Another critical limitation on their effectiveness was that since militiamen by their very nature were citizen-soldiers, they did not necessarily live close to where fighting would occur, especially if that were on the frontier. Moreover, the states jealously kept control of arming, disciplining, and training their militia and resisted having the men serve out of state. Though training was crucial, the War Department was limited to making recommendations and supplying training manuals. The Army could not enforce the type of rigorous training that had enabled Bvt. Maj. Gen. Winfield Scott to convert regular soldiers, some of them as raw as militiamen, into the professionals who had excited the admiration of even the British at Chippewa and Lundy’s Lane.