A common reason that pages are not appearing in search results is the presence of the attribute rel="nofollow" in page links. This attribute tells crawlers to not follow the link and to not record its contents. In short, if a link contains rel="nofollow", search cannot access it.
Many link generators will include this attribute, either by default or as an option you can select. If a certain page is not showing in results for you, visit a page where it is linked to and see if rel="nofollow" is present. If it is, edit the link and contact [email protected] to recrawl your site.
For more information about the nofollow attribute, please refer to Google's article Use rel="nofollow" for specific links