This is just beyond ridiculous to characterize the FB patents addition as some sort of social good needed in the battle against patent litigation, like they are doing everyone a favour. The patents addition in the license is there to protect FB's interests. Words that specifically benefit the interests of a megacorp do not belong in an open source license meant to be used by everyone and anyone. It sets a terrible precedent that can be used to justify a whole range of different companies adding their own clauses, each of which that can be plausibly argued for. And all of that requires other companies to conduct legal counsel, altering which companies would be adopting WordPress - imposing a kind of decision making process and barrier that few if any in WP would or should desire. And it's not even worth it considering there are equally attractive alternatives out there.
The size of React's ecosystem, bus factor and the availability of React Native all are nice but overstated in their importance relative to alternatives and obscure the many other considerations the WP community weighs up.
Further more, React's ecosystem size conveys marginal benefits given that use of React in core would have been constrained (it's not like core devs would be tapping into many additional React-based tools for core work).
React Native has not proven itself to be as stellar and promotes lock-in. If we come to rely on additional FB-engineered architecture to such a degree WP bets its future on the decisions made by a corporate giant with goals very dissimilar to WP and with decisions that may change down the line. This idea that FB has somehow has the closest thing to the holy grail and so we must all jump aboard the FB train is a very foolish and shortsighted one in my view. WP was wise not to adopt it.