Sorry, I am being unclear. I don't mean that GPLv3 gives you a patent grant for all implementations, yes. I mean that the willingness to license code under GPLv3 means that there's an upper bound on how much Open Whisper Systems cares about licensing the protocol for money.
Which brings me back to the original question—why do we think that OWS's pushing of Signal Protocol is about money? Yes, I expect that for Allo they got paid by Google to write and maintain some code. But I don't think that their general claim "Signal Protocol is good crypto for everyone solving this problem" is motivated by money, because so many people solving this problem could use the GPLv3 version.
Which brings me back to the original question—why do we think that OWS's pushing of Signal Protocol is about money? Yes, I expect that for Allo they got paid by Google to write and maintain some code. But I don't think that their general claim "Signal Protocol is good crypto for everyone solving this problem" is motivated by money, because so many people solving this problem could use the GPLv3 version.