Let us also not forget this is the infamous argument of, "Why does the United States need to spend so much on the defense budget?" To which there are a number of answers, none easy, but among them the largest are fronting global operations - we as the United States are more or less responsible for the defense of many, many nations and held accountable for performing defense roles in their environments rather than home nations having the capability or interesting - and that we as a country invest heavily on our research, development, production and fielding of new technologies. There are few militaries in the world that can even begin to field the same type of equipment in the same number as the United States; people tease, mock and belittle the F35, but there's no
actual competitor aircraft taking to the skies that can do what it does as good or better, let alone close.
Few militaries maintain a mission portfolio that accounts for anywhere and everywhere at just about any time so that need to fight a war at moment's notice is no coinless effort. Rare still, there are only a handful of countries that provide any level of care, treatment and sustainment for their members, in that while military day to day care is considered bad, it is really only considered bad in the United States where you could easily get better treatment in the civilian sector. Battlefield wise? There isn't too much competition for how much effort gets put into taking care of everyone as best they can.
We haven't even spoken to maintaining a successful nuclear deterrence operation, but the details go on and on. The real reason the United States is paying as much as it is, is because it is funding countries who "cannot be bothered" with their own national defense; the same reason President Trump hammered them so hard when speaking about NATO. These other details are not as big as that. If these allied nations got off their comfortable rears and actually did something militarily for once, spending more on it to compensate for our expenditures, we would not be spending nearly as much there. They need to be paying their fair share as
@mdk said as it is costing the United States a fortune.
Another not well known issue is that the Department of Defense covets its funding, by which I mean, everything in the world they plan for assumes they at least receive the same amount they did prior, if not more. The military does not function well at all without this and the system quickly breaks down when cuts are introduced at every level. Most civilians know nothing of this, or rather do not care because "war is bad" and clearly that is all a military is for, but it is
very difficult to retain military members in service in this day and age. The civilian sector offers just about everything better, almost universally in pay, benefits and hours, now including health care because it is mandatory and is not too much worse than the very low quality they already experienced (and rarely were ever able to use) along with the Department of Veteran's Affairs' provisions. Retiring and separating members are willing to take just about anything if it is only slightly better given their conditioning to lack.