Surely I can just list my achievements, qualifications and experience. Isn’t that enough?
Compare a Hyundai motor car with a Mercedes. Both have engines, a gearbox, 4 wheels and internal upholstery for the driver and passengers. Both will get you from where you are (geographically speaking) to where you want to go, and in the same time if you obey the speed limits. However there is a massively different perceived value between them, which accounts for the huge price differential. That price differential and difference in perceived value is derived primarily from the way the vehicles are marketed and sold, rather than any real physical disparity. It is almost certainly true to say, I think you will agree, that most people, if all other things such as price, were equal, would prefer and buy a Mercedes. This buying decision is made based on the benefits of the product (reliability, comfort, kudos) rather than on the features or specification (4-cylinder engine, synchromesh gearbox, 16 inch wheels etc).
It is just the same with a professionally-written CV. All other things being equal, do you think your future employer would prefer a Mercedes or a Hyundai? The only way he will perceive any difference between two candidates he hasn't met before, particularly if their qualifications and experience are similar, is by comparing the look and feel of their CVs. Unfortunately this initial appraisal is over in approximately 8 seconds, so he or she needs to be sold the relevant factors in that brief interval. In Sales language, the selector needs to be presented with the benefits of employing you rather than just the features of your previous experience and qualifications.
Your CV is your Sales and Marketing Document; your Product Brochure. Just as all cars are not created equal, neither are two individuals. However, unless the benefits to the organisation of employing you rather than the next person in the pile, are presented quickly and credibly to the "buyer", then he won't even consider the features.