Search engines don't do this at their own but if your robots.txt file encourages them to do so. Check your robots.txt file and see if there is something wrong with it. If it all seems okay with your robots.txt file. Then you can simply check for the plugins or addons you are using for SEO. Some add-ons/extensions have features to disallow indexing of a specific post or page. Therefore, you should check their settings and see if you can find something.
If none of the above steps help you in solving your problem. The last step is to ask a professional to analyze your site and solve your problem.
There are two reasons why Google can't index your site yet, maybe you are blocking them through your robots.txt and meta nofollow tags, and maybe your site is new. Mostly Google can crawl and index a new site from 3-6 weeks..
A long time ago, you just have to submit one page to authority social networking site such as Digg or Reddit to get the whole site indexed. You can try submitting a sitemap to the Google Webmaster Tool. Wordpress blog is easier to get indexed than static HTML site. Getting backlinks to site may also be a solution to help your inner pages indexed.