To my knowledge, most programs that served as commissioning and training sources for officers, with the exception of West Point, were established during or after WWII

That's actually not quite the case!

ROTC grew out of the US's experience in WW1 and the realization that 90 Day wonders were simply never going to be enough on their own to supplement the regular officers required by a full mobilization for war.

It had antecedents as well in both the Morrill Land Grant Acts and the Plattsburg Camps. The Land Grant Acts required that each of the new schools set up in every state include military tactics as part of the curriculum, understandable as the first act was. In many places this was curtailed to a few hours instruction(think the driving range on the Quad scene in Animal House. But at others it became a central part of the student body, places like Texas A&M and Virginia Tech were eventually elevated to Senior Military College status, while others like LSU, Clemson, and NC State were in this vein as well. This was also then supplemented by the handful of state military schools, like VMI, The Citadel, and Norwich who all had active duty officers assigned for instruction purposes even before the establishment of ROTC and regularly inspected by the War Department.

While in the summers immediately prior to US entry into WW1 senior officers and thinkers bemoaned the existing shortfall of military experience in the young men of America, and particularly that better off class who would be expected to serve as officers. And thus under the direction of General Leonard Wood an encampment was set up at Plattsburgh New York. Each summer several thousand young men would pay their own way and receive military instruction which was then certified and would place them in a position to be offered a commission usually, though many still went through the abbreviated OCS the Army established, which produced the much panned '90 Day Wonders' in both war.

Thus following the war we see the establishment of ROTC in the early 20's. A young man would receive a stipend if he earned one, and would be commissioned into the reserves, do a few years of active service, then go into civilian life with drills here and there, while proving a ready body from which to draw men to supplement the Regulars and ease the difficulties of mobilization.

The Navy was actually rather slow to get on board with the plan. In part because they were happy with the boys club of Annapolis to produce as many officers as needed for the fighting ships. Augmented as needed by reserve commissions for Merchant Marine officers. But 6 pilot units were stablished too in the mid 20's(Chester Nimitz was famously the CO of the Cal Berkley unit).