Why? We all tend to give advice that would work for us, with insufficient regard to whether that would work well for someone else.
Eminent job-search counselors are brighter, more driven, have more expertise, a more pleasing personality, and fewer debilitating psychological and physical issues than do the pool of people who need a job-search counselor.
That counselor/client gap is likely to be especially large with clients who need to pay for job-search counseling, for example, students who got free help from their college's career center but still haven't been able to land a job and thus sought paid help. Stronger job candidates are more likely to find good employment without a job-search counselor, let alone having to pay for one.
Unless an eminent career counselors is unusual, s/he isn't conscious enough of that gap or is insufficiently willing or able to create and supervise a job-search regimen that is simple enough, well-adapted to the client's strengths and limitations, presented slowly enough, and providing the usually-needed months of ongoing support.
Too often, the eminent career counselor dispenses the standard job-search advice that they learned from other eminents: professors, career book authors, and keynote speakers. That advice is usually," "Network and make direct contact above all. Only secondarily use headhunters and answer ads. And do it all aggressively for 30 to 40 hours a week." That would likely succeed if the career advice dispenser were doing a job search but usually fails when attempted by typical career counseling clients. As bad, the eminent counselor too often assumes the client "gets it," and so the counselor doesn't provide sufficient ongoing support or implies to the client that that shouldn't be necessary.
A side note: The below-average pool of people that come to career counseling engenders an ethical issue for job-search counselors. Too often, job-search counselors are paid to make a candidate look better than s/he really is. Thereby, if successful, job-search counselors/coaches are in the business of replacing more qualified applicants with less qualified ones. That hurts not only the more qualified applicants but the employer, co-workers, and because the result will be worse products or services, society.
It may seem ironic for me to say all this. After all, I'm in my 27th year as a career counselor/coach. I've addressed those ethical issue by focusing my efforts on helping clients choose a well-suited career and on making the most of their current job. I accept clients for job-search counseling only when I honestly feel s/he'd be a great candidate for a job but merely needs advice on how to present him or her self fairly and that s/he'd be better off getting that counsel from me than from a more entry-level career counselor or from a trusted friend.