The inherent problem with creating a new browser/platform is getting people to create addons/extensions for it.
If you don’t think Google could do this, think again. Google has an iron grip on the Chromium project.
From the beginning of its time with Google, Android was touted as THE open-source phone operating system. The Android Open Source Project was used by several projects to create their own version of Android.
Then at a certain point, Google introduced an app called Google Play Services. This app is not open source and contains all of the stuff you need to access Google’s services.
Yes, this seems like a case of not caring about non-chrome browsers while making sure the API only works with their own client is actually a security benefit for their users. Lets not forget that many people use the sync feature as a password manager, so from Google’s perspective at least this is quite a security issue.