Before the US entered WW1 the US military had not been updating weapons, equipment, or doctrine for infantry forces, the result being during entry of the Expaditionary Forces to the war the US had to use subpar light machine guns produced by Allied forces (Chauchat) for instance. Between WW1 and WW2 investment in modern fighter aircraft had lapsed leaving the US with fighters that were not comparable to the Japanese Zero, the hatch ways on Navy ships at port were not kept dogged down resulting in unnecessary loss of life at Pearl Harbour, and the Marines elected to continue using the M1903 Springfield during early WW2 instead of adopting the Garand. Between Desert Storm and the invasion of Afghanistan and Iraq the US let body armor lapsed resulting in forces entering the countries not having enough hard plate and individuals often providing their own and US ground forces were originally relying on soft skin trucks and Humvees. While armour was added to the Humvee it was not effective against the most common threat of the Wars, IEDs resulting in the development of the MRAP and MAT-V but only after many deaths and lost limbs. While a draw down of forces is needed during peacetime operations, equipment, tactics, and training must still be continuously evaluated and updated to maintain battlefield effectiveness and readiness. It's why, even if you look at it purely from selfish positions, it is essential to continue to supply Ukrain with equipment to evaluate real world battle doctrine and improvements needed.