They employ professionals. Because anyone can operate a word processor many of us think that therefore you can write a resume or CV for ourselves. While it is clear that we can enumerate the achievements, qualifications, previous employers and so on, and perhaps with a touch of artistic design (which is certainly the worst that can be applied to a CV), only a professional has the ability collect this information and present it in such a way that gets through the door with an advantage in any competition. It would be folly to entrust something as important as getting your next job or change careers to anyone who is not a professional. 2. Certainly, I can only my achievements, qualifications and experience. Is not that enough? This is not related to, and partly explains the answer to question 1. But dig a little, this is like saying that it is sufficient to present the specifications of a new car to a potential buyer and we hope that only sell the product.
Compare a Hyundai with a Mercedes car. Both have engines, a gearbox, 4 wheels and interior trim for driver and passengers. Both will have to from where you are (geographically speaking) you want to go, and at the same time if you obey the speed limits. However, there is a perceived value massively different between them, which explains the huge price difference. That price differential and difference in the perceived value is derived primarily from the way vehicles are marketed and sold, more than any actual physical gap.