Websites with rarely-updated, static content leave site visitors with no reason to return, let alone bookmark. Visitors are not likely to revisit your site again if your site presents itself as little more than a brochure. Generally speaking visitors want relevant information that speaks directly to their needs, and assists them in making a buying decision.
Additionally, search engines such as Google, Bing or Yahoo! use algorithms that will sink a site’s ranking if it is not updated often.