Multiple users could be led to think incorrectly (and this has a name in the dictionary) that a search engine indexes every page from the available content but some of the known, popular names today do employ a policy with similarities to page directories. Why? Because they establish subjective methods to qualify pages and that means to obscure content if it doesn't fit in that consideration of appropriate. If someone doesn't like it, it might not be indexed being manually rejected.
Even when the description of the search engine could be something like this, from Google:
"Search the world's information, including webpages, images, videos and more."
It's false as some of that information is not available due to the aforementioned interests of showing only some pages to users. “Search part of it” is ok. It doesn't happen with obscene imagery though, software piracy at the organized level or other information that truly could create social issues of relevance but it's true that different industries provide a great source of revenue for those companies primarily based in unsolicited advertisement.
It also a problem when the search algorithm shows more results than real, saying that it finds 100 and there are only 60 or less. It's an illicit deceit to misled users to think that there's a better efficiency.
Another illicit curiosity when the interest of revenue finally surpasses any kind of ethics appears in perceivable actions against the own direction of the companies. Then some policies say “don't do this” but at the same time the company does it every day. It happens with obscene material for instance; several search engines pretend to be worried about this in their policies but they facilitate the content since multiple major engines are "pornography search engines" where each person at any age would find whatever obscenity, even suggested by the own algorithm. That safety systems are to turn between a porn search engine and a filtered engine, right? Not very hard to dupe at the same time charging a great responsibility to educators.
Did you see some YouTube videos and their obscene reference image? Try using these keywords “win compilation” and you should see some erotic / obscene material subjectively tagged “for all audiences”.
It's incredible how in this state of the evolution the advertisement creates fortunes giving economic power to entities with the surprising idea of forcing users to view advertisement. Well, you could use a plug-in like adBlock but nowadays there are millionaire pacts to filter some and some not after besieging developers of such tools, against the free competency, where who has more money to spend can have more satisfied content publishers and revenue.
As a model of execution, if someone reads this article could mark this page to be out of the directory so the “search engine” doesn't display it like others, independently if someone could find it useful or it is also “Internet network's information”. Like a child's tantrum but with the power to do it and without contemporary legislation to avoid it.
As an unmade road yet, Internet is pretty young so let the opportunistic entities exploit the precariousness of rules to protect all the damaged parts although this situation should change soon.