I'm told that one reason companies might have chosen to avoid React was that they could have imagined themselves be in competition with Facebook at some point, and thereby in the danger zone with their old BSD licence.
Even being on the back-foot when having to defend your patents, by refactoring React out of your application, was apparently damning enough for people to migrate.
If you're ok with trusting a direct competitor not to misbehave, then sure, use React under those terms while competing with FB. But large companies consider their patent portfolio to be a significant strategic asset, so it shouldn't be surprising that their legal counsel advises against accepting such a clause.