The first is basically LinkedIn spam at this point. It's typically an outsourced operation (can be several layers of outsourcing for larger organizations) where the "recruiters" are given keywords to match with profiles and a set of canned response to literally copy-paste in the chat. The point is simply to have a steady incomming stream of resumes of people looking for a new job. When there's headcount they might start sending automated messages advertizing recruiting events.
The second is, well, a network of recruiters where nobody is a "recruiter". They are "headhunters", "talent acquisition lead" or just "involved with hiring". It's when your friend insists on buying coffee a week before the next funding round of the startup he works at is announced and he is curious if you like your current job. It's when you make a few referrals for a new project before headcount is officially announced (watch out for the commission!) and so on.
Only one of them matters.