Same as with "crypto" which doesn't have any more to do with cryptography either...
I wonder if that was a side effect of all the William Gibson style scifi gaining a browser audience.
Originally, the "cyber" in "cyberspace" was clearly from "kybernetic", focusing on the " virtual worlds", AI, mind uploading ideas, etc.
But the actual plot of e.g. Necromancer heavily involves hacking, warfare and all kinds of topics that would be relevant for cybersecurity today.
So maybe "normies" learned to associate "cyber" with hacking instead of the kybernetic concepts it came from.
My theory is this: Until recently, "cyber x" meant the same as "Internet x" (because Internet ≈ Cyberspace), except that "cyber" sounds a bit cooler, and security organizations wanted to sound especially cool, so they were the ones who used "cyber" most, causing the shift in meaning.