To put it concisely, “why is having a patent license until you commence litigation worse than not having one at all?” The answer is subtle.
Many corporate lawyers operate on the assumption that all open source licenses that do not mention patents (BSD, MIT etc) implicitly grant a patent license. Clarifying this ambiguity is seen by them as harmful — that’s why approval of CC0 at OSI was abandoned[1], for example. Including an explicit patent grant removes the possibility this could be argued in court and is seen as an escalation of the patent conflict by Facebook.
Given many voices at Apache are being quietly guided by corporate counsel, this seems the most likely underlying explanation for the antipathy that's been rationalised out into the open.
Many corporate lawyers operate on the assumption that all open source licenses that do not mention patents (BSD, MIT etc) implicitly grant a patent license. Clarifying this ambiguity is seen by them as harmful — that’s why approval of CC0 at OSI was abandoned[1], for example. Including an explicit patent grant removes the possibility this could be argued in court and is seen as an escalation of the patent conflict by Facebook.
Given many voices at Apache are being quietly guided by corporate counsel, this seems the most likely underlying explanation for the antipathy that's been rationalised out into the open.
[1] https://opensource.org/faq#cc-zero