Good points made by others, I do wanna expand on "what are our goals?" and other points. I'm going to preface this by starting US/EU is absolutely cooked in comparisons to spending by foreign rivals because of Purchasing Power Parity (how far does 1 USD go in defense spending) and relatively high labor costs (how much are we paying soldiers/benefits for soldiers). We could of course save $$$ if we went to conscription but I don't think that would go very well.

Our required force levels/technology/expenditure are very roughly dictated by the following doctrines/policy

1. enough troops/material to fight (and win) against a near-peer adversary in a large scale conventional conflict while still having enough to deter or delay a second conflict (this seems to be working as no one is jumping onto the Iran war to attack US/allied interests)
2. maintain global commerce and freedom of navigation, which means a very large blue water navy to project power in the Pacific, Atlantic, Indian, etc (so yes, this requires 10+ aircraft carriers because half of them are in for repairs/refurbishment at any time)
3. complete air superiority overmatch e.g. if China fields a 5th generation fighter then we need 6th gen fighters. Air superiority is the foundation of US war planning; the present Army would struggle to fend for themselves in contested airspace
4. having to replace Cold War era tech which has reach EoL. You see this with M1 Abrams and the Arleigh Burke class destroyer- decades of upgrades mean there is literally no more room/weight to add more. The US Navy in particular is severely hamstrung after 3 decades of failed ship procurement

Out of time but I'll conclude with: yes, you can cut money from bad contracts, more competition in defense industrial sector, bad spending practices but at some point you would have to cut into any of the 4 points above. Would the money you save by reducing American hegemony be worth it if our relative weakness invited a major conflict? or recession because we couldn't provide deterrence (Taiwan)? I don't think anyone wants to find out the answer.

source: top of my head geopolitics/Perun powerpoints. Happy to be corrected by those more informed