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.
deleted by creator
Yeah as shown marked in the screenshot Chrome will get buttons or other options to delete and restore search providers.
This change was made because people deleted search providers and there was no easy or official solution to bring everything back except creating a new profile or mess with some config files.
What are the standard search engines?
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.
