Google Chrome Vs. Chromium

Google Chrome is currently the most popular browser on desktop PCs. It has over 54% of desktop users usually in the Windows world choosing it over the other browsers. Here in the Linux world, Google Chrome is not the most popular as most distros prefer to ship other web browsers. The most popular of these is Firefox whilst others prefer Chromium. Chromium for all intents and purposes is very identical to Google Chrome. They share everything from looks to extensions, engine, and features. So why don’t they (Linux distros) just ship with Google Chrome? What are the differences between Google Chrome and Chromium?