Google Ads was born out of a need to monetize search traffic. In the late 1990s, Google’s founders, Larry Page and Sergey Brin, were struggling to find a way to make money from their search engine. They came up with the idea of selling advertising space on their search engine results pages, and Google Ads was born.

Initially, the idea was met with skepticism. Many advertisers were hesitant to spend money on online advertising, and Google was still a relatively unknown company. However, Page and Brin persisted, and in October 2000, they launched Google AdWords.

Honestly didn't know they waited 4 years before monetizing anything

Edit: for those who'd like this source but Wikipedia says similar and, of course, if anybody finds a counterfactual I'd be interested: https://www.webmonster.com/the-evolution-of-google-ads-past-present-and-future/