Fuchsia is literally a Google project to avoid using Linux.
Look at their other "Open Source" projects like Android to understand why they would want to ensure they would avoid GPL code. It's all about control, and appearances of OS through gaslighting by source available.
Fuchsia would be far more valuable to everyone, including Google, if multiple parties participated in its development. If control was all that was desired, a hard fork of Linux would have made more sense. GPL doesn't compel companies to work with upstream. Just because you don't understand why fuchsia exists doesn't mean you need to invent fiction about it. Is it hard to believe there might be technical advantages to an alternative architecture to Linux and that a company might be willing to invest in trying to bring that innovation to the world?