- congressional oversight increased, with the result that the purchasing authority is no longer generally the end user. We aren’t just buying a ship (plane, gun, etc.), we’re maintaining a logistics and manufacturing industrial base to produce that type of item (and maintain jobs in congressional districts). So maybe we should buy a few more tanks/ships/bombs than we need so that we don’t forget how. (A bit dubious, but it’s one of the reasons we make the funding decisions we do.)
- risk tolerance shrank. Especially in war time there was a high tolerance for risk if the payoff was big enough. These days our risk tolerance is basically zero. I once had to get an admiral to sign off on a risk hazard assessment with an estimated likelihood of ~1e-18 (you’re more likely to win the powerball jackpot twice). There was a cap that might pop off an item at high speed during flight, and if it hit someone they would probably miss a day of work. By the likelihood/consequence framework for risk management, that meant it required an admiral’s signature. You can’t move fast in an environment like that.
- complexity increased. Old schools systems like a WW2 jeep were designed and prototyped in 40 days because they were incredibly simple and made liberal use of COTS parts. There’s an argument to be made that maybe we don’t need such complex systems to meet requirements, but I don’t think anyone is arguing that we should be replacing all the F-35 fleet with a WW2-style aircraft. (Although there have been proposals to build super-simple aircraft for CAS missions, etc.)