Any given advertising message must compete for the reader’s attention. The paper may contain hundreds of ads, as well as dozens of articles and features for the reader to wade through. If the total time spent scanning a newspaper is only 20 minutes, your ad may not be noticed by a significant number of people.
You have no assurance that every person who receives the newspaper will read your ad. They may not read the section you advertised in, or they may simply have skipped the page because it contained little or nothing else of interest.