The thing is Linux underpinning Android and ChromeOS is largely relatively irrelevant for the Linux community. It's convenient now and again, but not many of us rely significantly on either of those for our use of Linux. Replacing those uses with Fuchsia would mean nothing to me, for one.

In any case, given Google's lack of attention span, I suspect Linux will still be going strong another 4-5 new OS's from Google down the road.