SEO professionals and webmasters often visit Google Webmaster Help to find solutions of the challenges they are facing. Recently, a webmaster posted that the search engine is not picking his website markup and thus, rich snippets are not visible in search results. Zineb, an employee of Google replied that the search engine giant does not show rich snippets for all the websites. He clarified that having markup do not make any changes to Google's policy.
The answer should not surprise you though. In December 2013, Google decreased the rich snippets displayed on the SERPs. So, don't get anxious if rich snippets for your web pages are not exhibited any more.