If you want to get your browser to work with popular sites you need to provide an easy way for the web designer/developer to ensure that their site easily works

If you want to get your browser to work with popular sites you need to provide an easy way for the web designer/developer to ensure that their site easily works with your browser. Providing the necessary developer tools in the browser, puts zero barriers on the designers/developers to debug rendering issues with your browser. Having a more complicated way to get access to such tools could make developers say, "it's too much work to develop/debug for browser Y, we recommend you use browser X instead."