Why do search engines take external signals into account?

Search engines take external signals into account because this is a way to understand how a site is evaluated by others, not only by itself. Here is why this is critical:

#1. Links are like recommendations

If other sites, especially authoritative ones, link to a page, this is perceived as a "vote of trust". In essence:

"If others consider this content valuable, it probably deserves attention".

#2. Popularity signals

Mentions in the media, blogs, forums, and social networks are markers that a site generates interest. Algorithms see that the content lives beyond the page itself, which means it is relevant and active.

#3. Harder to fake

On-page optimization can be "drawn up". External signals, however, are harder to control. That is why they are considered a more "honest" indicator of a site's value in the eyes of others.

#4. Separating quality

Millions of sites write the same thing. But some have 5 links, others have 500. This helps the search engine rank pages by authority, not just by content.

Put simply, external signals are a site's social rating. And the search engine trusts it more than the site's own self-assessment.