Copyright was established for the benefit of publishers, not authors. In the 1600s publishers were licensed, as part of a censorship system; the point was to only give licenses to publishers who followed the censorship rules. It was quite profitable for the publishers because they faced far less competition than they otherwise would.

The censorship system was abolished but the publishers wanted to keep the licensing system, so they came up with a new idea: licensed monopolies to publish specific books.

Exactly right. Karl Fogel's excellent write-up recaps the history: https://questioncopyright.org/promise/index.html