Huh? Why would you switch to miles from kilometers?
And IMHO megameters aren’t used that often because there is rarely anything useful to measure with it. Using a different unit makes you lose your sense of scale (e.g. the earth has a radius of ~7000km, not 7Mm) and for astronomy megameters aren’t big enough most of the time (and you might as well use lightseconds/years because gigameters give no real intuition of scale).
Why do you think that? Dive bombing hits generally within a few meters, even during WW2 where it was used against tanks. Why would a guided rocket be that much better? Where would it get the target data from if it doesn’t have a human to guide it?
Obviously, there exist guided munitions with higher accuracy (<1m) but that’s not the majority.