Google owns the vast majority of the web search market. When a single company dominates any market it often results in:
An Inferior Product - Since competition is not constantly spurring innovation it is easy for products/services to stagnate.
Even if a company is pushing forward with innovation the lack of competitors using innovative methods to improve search may result in a myopic focus on micro gains within existing technologies.
Inferior Customer Service - Since there is no alternative, customers are forced to work with the company on it's terms.
Gilad Edelman. Google's Antitrust Cases: A Guide for the Perplexed. wired, 12/18/2020.
Includes link to download entire complaint that has been filed by DOJ.