Ultimately, the structure of the modern corporation was allowed to take on a lot more complexity due to the advent of computers. So, we have fewer roles where people do full-time work managing inboxes or whatever (though not zero, because that is essentially what my wife still does for work), but more roles have an "inbox management" or other secretarial component to them now.

In practically every job, it became the case that you're also a part-time secretary. Assistants became mainly a luxury reserved for fat cats, and the rest of us plebs are buried in emails.