No browser can search more than a small fraction of what is online, so there is a chance that your search will miss something critical.
Many websites are sponsored by organizations hoping to make a profit or to sway public opinion on an issue. In either case, the information is sure to be biased.
Anyone can create and post a website, regardless of their credentials or trustworthiness, so you can’t be sure the information on a website has been peer-reviewed or evaluated by experts
Many organizations post press releases (which always present one side of an issue) on their websites