Rather than answer a philosophical question such as that, let's answer a more concrete question: what is among the most important factors that helps boost search engine rankings? The answer would be link building. When they are scores of valuable links distributed throughout the internet, the positive impact on a website's rankings would be difficult to ignore. Keep in mind the fact that each and every linked placed on the internet acts as a vote for a website's popularity. The more links that are amassed, the better the ranking of the site will be. This is why working with link building services is so highly recommended.
Now, some will wonder why it is necessary to work with link building services. Why not just randomly trade links or purchase hundreds of them from low cost providers? Basically, there is really no value to a process such as this. There are different grades in the quality of links. Links with low value present little benefit while links that are of high value can boost a website's ranking significantly.
Links of high value will be those placed on popular sites that experience a great deal of traffic. These sites will also have a decent Google Page Rank and will be positioned at an impressive ranking in the search engines. Also, it is important that the link is placed on a site that is similar to the content of the site the link points to. Such a process is known as relevant linking. When a link is placed on such a site, the search engine robots will take note of it. This will lead the robots to properly ranking the site that the link points to.
Additionally, there will be the side benefit of the link delivering direct traffic since it will be placed on a popular site. Consider that a helpful "fringe benefit" in the link building process.
Would these be the only reasons to work with professional link building services? Actually, there are quite a few more.
When links are added to the internet, the process needs to be a slow one. The search engines generally look down upon the placements of dozens of links all at once. This is a red flag that the links are not organic and more intended as a form of advertising. Link building services will slowly add links to the internet over an extended period of time. The search engines prefer such a process and will smile upon' such a link building strategy. In other words, the ranking of the corresponding website will be more preferable.