ASF's license limits it's scope. ASF software cannot carry dependencies on licenses that have wider scope than their license. In addition to the scope, the FB license is very one-sided.

As such, ASF decided to disallow FB licensed dependencies. One particular ASF project did not have an alternative, so they asked FB to re-license. FB agreed to do so.

Because it was easy, and because the positive talk surrounding FB's license seemed to intimate that FB's intention was the same as ASF's license intention, they requested FB to relicense react so that it too could be included as a dependency on ASF projects.

Faced with making a decision, FB determined that their licensing strategy associated with litigation was more important than their ability to be included in ASF projects.

A lot of eyes were watching the request, many hopeful that the FB decision would justify and clarify their interpretation of the FB license and it's intentions. FB disappointed them though, and basically said "bugger off if you don't like it. We'll lose people, but we don't think it will be that many."

Judging from this discussion - and the fact that HN is one of the most pro-react communities around - this decision will not play out kindly and could be the death-knell of react's position as a major force in UI development.