Relevant Chromium issue ticket is here.
Before people cry, this change was done because people deleted the pre-installed search engine selection and had huge troubles restoring it because there was no option given. So this was done to improve user experience.
They research some solution to provide maybe some buttons or other mechanism for restore deleted providers.
Same like in every other browser, google, duckduckgo, bing etc.
The decision to make them the default and then pre-configure them is based on statistics, they estimated what people use. And this is google, bing etc. This is why every bigger Browser uses them. There are also variables like cooperation, sponsoring etc.