Earlier quoted context omitted.
Sounds to me more like the Apple Vs. Google "ecosystems". Sure, Google has a Play store and a competing OS, but it's not like you can't find Chrome in the iOS store.
its interesting that you picked chrome as an example, with it being a wrapper around Apple's webkit on the iOS platform
Different HMDs are arguably more similar than different GPUs, and they manage to support the same software, but in the early days there were plenty of Glide-only games. That didn't work out so well. Most people will probably just use tools that optimize for any popular HMD with little enough effort that only contracts will make exclusives make sense.