I could be wrong as I was young and not yet in the field, but my impression has always been that sometime in the 80s/90s as the whole "networking, world wide web, wowie!" moment happened, there was this idea that "maybe on a local computer everything is files, but on the network everything is streams. Hey, maybe everything is streams!?" and C++ just happened to be creating itself in that zeitgeist, trying to look modern and future-thinking, so somebody decided to see what would happen if all the i/o was "stream-native".
IDK, it'll probably make more sense in another 15 years as we clear away the cruft of all the things that tried to bring "cloud native" paradigms into a space where they didn't really fit...
IDK, it'll probably make more sense in another 15 years as we clear away the cruft of all the things that tried to bring "cloud native" paradigms into a space where they didn't really fit...