The US only has a shortage of Javelins because they have sent so many into Ukraine. In the past half a century the US hasn't had to supply a military conflict as it has with Ukraine v Russia, and almost nobody in a position of power (including across Europe) on the planet was predicting Russia's invasion. The notion of literally planning for every possibility is absurd, and if the US military tries to do that regarding a budget, it'll just get that much more flak for spending policies.

Armchair Internet users will proclaim the US military should know all and see all and know exactly how many Javelins it will need based on knowing every single conflict that will happen before it happens. And if they make a mistake, and spend a lot of money on weapons they don't need, then they must be attacked for the ridiculous spending. The armchair crowd can't have it both ways.