It's not just big companies necessarily either. Say you are a small startup working on something really innovative and you have a patent on part of your work. Facebook decides to build something similar, violating your patents in the process, and they are going to put you out of business. If one of your core technologies is react under the BSD + Patents license, then you are screwed. You can't sue to save your business because even if you do you have to immediately recall all of your software and replace React.

Sure, not everyone is in that situation. Facebook is big enough though that if you have any patents you have to be _very_ careful about that license.