Other search engines will show you ads to make money. Search engines will target you with ads in two ways.
The first is based on your query. Advertisers can target ads based on keywords which are similar to that search query.
Second, search engines use a variety of technologies to track your behavior and build a profile of you as a user, which can then be used to target you with ads.
Other search engines (not Neeva!) use cookies to track what you’re searching, what websites you visit, and what kind of ads you click on. Doing so allows them to use your history to build a profile on what kind of things you like to see and serve you ads targeted to those preferences. The data you create online is used by advertisers to build a profile on you based on websites you visit, ads you click, and a number of other sources. The profile is used to show you ads targeted to your behavior to increase the likeliness of you clicking on the ad.