The People block is a very old block which dates back to the time before we had a navigation block or a navigation drawer. Thus, it was needed in the olden days to provide a link to the Participants page. Nowadays it is no longer needed because there is a Participants link in the navigation drawer (Boost theme) and in the navigation block (Classic theme).

Thus, to simplify Moodle a tiny bit and reduce the long list of blocks, I suggest that the People block is removed from core and added to the plugins directory.