> The developer effort is not wasted because it's open source. Anyone can fork it at any time

Assuming you can get a hardware vendor to support your fork.

Android has always been a weird blend of proprietary BSPs wedged together with the core AOSP project - we used to have an entire team whose full-time job was merging the Qualcomm BSP into our AOSP fork. At the time you didn't even get access to that BSP without inking a deal with QCOM...