Perhaps the Ferengi military scaled back from one which roamed through space in early TNG to a defense force which patrols strictly within Ferengi Alliance space later on. The reason for this could be simple, the military demanded pay premiums per every light year outside Ferengi space, plus danger pay every time they got into a hostile situation with a certain percentage depending on who they fought (an extra 25% if they went against the Federation, 50% if against the Romulans, 75% if Klingons 90% if the enemy was a first contact). Eventually it was decided that it wasn't worth paying so much money, so the military just patrols Ferengi space. The crews of the ships don't get paid extra since they don't leave Ferengi territory, and in home space there's less of a chance of running into enemies. Since military life is no longer profitable, recruitment's at an all-time low.