Emphasis mine.
This has never been a thing in a core MM. Even the 2E MM -- one of the best -- didn't do that, it just told you how the monsters fit into the world. The CR system was an attempt to provide a tool to help GMs judge the encounters they built, which previous editions had just ignored or told the Gm to roll randomly so you might run into 3 orcs, or 300 (no, that is not an exaggeration). So, CR isn't perfect but it is an attempt to provide the GM with some information D&D has never really provided, and almost no other games even attempt.