I get that Apache and GPL are well-established (perhaps not GPL3 yet though?), and that encourages stability to use them.
But this new patent license is stronger. If it would make the industry safer from patent armageddon in the long term, it might be worth the effort to popularize yet another license.
The reason is not just that Apache is well established, it's that it's sane in its extent.
Let's say 10 years from now Facebook decides to go on the warpath over fairly bogus patents. The EFF puts the headline patent on their Most Bogus patent busting list and then puts out the cry for "who is with us?"
No company using any Facebook open source code answers.
But this new patent license is stronger. If it would make the industry safer from patent armageddon in the long term, it might be worth the effort to popularize yet another license.