I haven't torn down one of Castle's controllers, but I suspect that they don't do the cycle-by-cycle current limit that you would need to achieve this. To do so takes some extra circuitry (little dinguses called comparators, some current sense resistors, and some logic gates), a controller chip with hardware that knows what to do with the signal if a comparator notices that the current is over limit, a moderate amount of some hardware engineer's sweat poured out in the development lab, and software that knows what to do when the controller chip shuts things down. When you're all done adding that, if you use a motor with too low of an inductance or if you get a short circuit at the ESC output then it all goes up in smoke anyway.
That more-capable controller costs more, may be bigger, and may consume more power. The other extra circuitry certainly takes up space, adds cost, and robs a bit of power.
I'm not trying to apologize for Castle, but -- out of curiosity -- how much extra would you spend in money, size, and weight, for a controller that's guaranteed to not go up in smoke in the event of a prop strike?