I have never got a job through LinkedIn, even though I get loads of contacts from recruiters - as many as 10 per week. The problem is that those contacts are poor quality. They are spammy as heck, basically mass emailing anyone who has a specific search phrase anywhere in their profile. For the last year my profile bio has opened with the statement "Recruiters: Please tell me what your favourite colour is if you want…
If they can fill their roles with acceptable candidates without reading individual profiles, what's their incentive to do so? Do you want a new job enough to be inconvenienced by recruiters? If not, then this system seems to be working perfectly.
Most recruiters have one goal, get candidates into a job - any job. Then they get their fee. They do not have an obligation to get a candidate in to the most suitable job. In my experience they will happily lie, flatter and cajole you in to doing their bidding and taking a job that is not right for you.
I don't want to deal with recruiters like that and that's why I try to filter them out.