That’s a great example of how you always have to design for a context.
For example, cars have "fail open" brakes but have independent cylinders so that it is relatively hard to have all four wheels fail at the same time (older cars had single master cylinders) - and one of the tradeoffs is that people want cars to get going immediately and not wait for brake cylinders to "charge up".
As more and more things get computerized, you have more options for "intelligent failover" - anyone who used to drive an old manual car knew you could slow down using the engine - but now the computer could detect brake failure and do things for you to help recover.
And as seen from other comments, the modern US military prioritizes "on-road safety" over "under ongoing attack ability" - partially because of changing strategies I suspect, but also from the realization that the US military kills more members of the US military each year via accidents, etc, than anything else.
You can use engine braking in automatic vehicles too, by simply changing to a lower gear.
An automatic one will not, and will hold the current gear until car speed falls within shifting range.
Ask me how I know :)
This of course meant the entire cars safety and stability control systems, ABS and traction control were all disabled. It drove like a tank.
The fix, obviously, was to replace the brake booster primer pump (hybrid car). It had worn enough to no longer recalibrate. Still perfectly functional, and would have kept working for a long time, bit it wouldn't quite meet the factory expected parameters so it failed it's test.
It appears that ZF 4HP20/4HP22 gearboxes can do this an unlimited number of times without apparently being damaged, but I'm not trying it on either of mine.
And emergency brake that's wholly separate circuit.