This answers the question from a management perspective. Facebook has a lot to gain from a small number of huge success stories like React. This makes up for the cost of all the failed little tooling projects.
Your second paragraph is an assertion -- maybe it's true that one project like React makes up for all of the failed initiatives that the author describes (i.e. multiple person-years of effort), but that's a claim that deserves some evidence. Even if it's true, there's a level of management implied, or else everyone would spend their work hours chasing the same, captivating rabbits. My suspicion is that there's a lot more selection happening inside Facebook than the author lets on.
From experience, it's easy to get to a place where you have a lot of smart, well-intended people working on things that just don't matter. Saying "the best projects win" doesn't really solve anything, because you still have to define "best". Either that, or it's true that this is just a "champagne problem", and the Facebooks and Googles of the world can just throw dollars at anything, in the hope that something sticks.