Reality is that the US defense industry is money-focused. It has become that way because we've not had to actually fight anything on our own soil nor really project power in a meaningful way for more than 50 years. Even Vietnam was not really that, nor was Korea, never mind all the smaller stuff.
Why?
Because its always been, in those cases, somewhat else's problem in the main.
Look at the defense industry around any of our larger military installations. They are all designed around "better, perhaps faster, but always more expensive." THAAD, for example, is roughly a billion per battery and about $13 million per missile. A single Patriot is somewhere between $3-5 million depending on the variant and again, the entire battery including fire control and such is close to a billion each.
Our "defense department and industry" considers a variant in development for use against "air-breathing" threats "cost effective" although those are estimated to come in between $1.5-2m per shot -- and not yet available.....
This against drones that can be fielded for a few hundred dollars a crack up to perhaps $10-20,000. Each of those carries perhaps a half-dozen or less (anti-personnel devices, small and cheap) to a hundred pounds of warhead (aimed at infrastructure and commercial transportation.)
These are all buildable today from commodity parts, are extremely cheap and inertial + GPS navigation, plus inexpensive machine-vision means they're true "fire and forget" sort of weapons. All it has to do with the first two is get close enough to be able to see whatever it is intended to hit and an enemy, whether foreign or domestic, could trivially launch a thousand of the small ones for under a million dollars -- or $10 million for the larger ones!
We have exactly zero capacity to knock down anywhere near a majority of such a swarm attack, say much less all of them and the larger, infrastructure-targeting capable ones can easily have ranges in the few-hundred mile area meaning they can literally come from anywhere all any time.
Civilian infrastructure and transportation simply cannot be hardened sufficiently to withstand such strikes and survive. It is both cost-prohibitive and in many cases physically impossible. For example, protecting power grid access in a city against such an assault simply cannot be reasonably done; the attack surface that you can be hit is too large and impossible to successfully defend. If the goal becomes to go after people in authority instead of infrastructure it becomes even more-impossible; a machine-vision system that targets law enforcement or fire department personnel, as an example, would lead to empty streets in both cases as soon as the people employed in same realized what was going on. Exactly zero firemen are going to go extinguish a fire if they begin to come under attack by small drones that can approach at five times a man's running speed, ram their target and explode.
Eisenhower warned of precisely this, that our military's supply chain would become intertwined with capitalist interests and corrupted leading to shooting at $20,000 drones with $4m interceptors. There is no way to win that fight for more than a short time. Reality in all conflict, whether civil or otherwise, is that money and "better technology" is always overcome with raw numbers if the numbers are far enough in your favor and you can do damage of importance to anything with said numbers.
War has always been about material and logistics all the way back to chucking spears and a failure to recognize when those logistics and weapon options change has frequently through history wound up being the last mistake you get to make.
