It's also one of the few that actually use humans to do the classification of entries and, understandably, it builds up a considerable backlog of entries for this reason. The other search engines, however, are largely automated and there is no obvious reason why automation can't be expanded virtually indefinitely to classify more sites. Yet many of these automated systems have delays of up to two months to have yourself entered into them - if indeed you never make it. Consider, that all of these ventures are businesses. Businesses, rightly, are driven by profit.
Profit is income minus expenses.
The income for the search engines at the present time comes almost exclusively from the advertising that they carry on the pages. The total advertising income that they can expect is a function of the number of people who visit the web site and the amount of money they can charge for each banner seen. Therefore, any sensible search engine does its level best to become popular and to be seen by as many people as possible because this is one of the main determinants of its income. However, increasing visits is a highly competitive and fairly slow process. Therefore, in the meantime, most are likely to be forced to focus on the cost side of the profit equation.