The big problem is that most recruiters on LinkedIn claim to have read your profile, but actually haven't.
My profile might contain my experience as a train driver (that's not what I do, but take it as an example). I say "No more train driver roles, please. I'm bored of being a train driver and I want to branch out into train maintenance".
10 messages a day offering me train driver jobs identical to the one I'm currently doing. They have a "great client" lined up and this is "a great opportunity for someone with my skillset". This message has been sent to maybe 50 other train drivers hoping someone will bite. A colleague of mine received an identical message from the same person an hour after I did.