Chrome was based in Webkit in it's rising years - which put it on par with Safari and Android. This meant that you could develop comfortably and do less cross-browser work up front.
Developers got comfortable. Chrome is open source, extendable, and keeps up with web standards.
No, Chromium is open source. Chrome != Chromium. There's still some secret sauce being thrown into chrome that you don't have access to.
> extendable
Only with JavaScript. It bugs me a bit to this day that this is deemed to be sufficient by Firefox as well. We've lost quite a few good extensions with this change.
> web standards
It helps that Google's team pushes most of those web standards, meaning that everyone else is typically playing catch up.