Let's try to put ourselves in the shoes of the search engines of the owners and creators. A few years ago to introduce a directory of thousands of other sites require much work, time and determination. After the software and scripts online, which automatically send pages to the directories are presented, making hundreds or thousands of links in a short period of time is not a problem. At the same time, the number of sites grows daily and the competition for particular keywords. Search engines have to find sites that best match the search phrase among millions of sites.
Due to the above factors, the creators of the search engines were forced to use special filters. In his opinion, on the one hand, the influx of large numbers of useless links of sites submitted to the thousands of professionals is limited and attention is focused only on showing the actual quality of the page. Moreover, only those sites that best fit the theme of the search, is back. Therefore, today it is better to have our blogs one or two quality sites of a hundred useless directories. At the same time, much attention is paid to the optimization of keywords, which remains the main factor in determining the site's theme.