I don't know. But I sure as hell don't believe they released this obviously dated tape to convince anyone that Zawahiri was still alive.
Yes they did. What, do you think they released Zawahiri's poetry reading right now just for the halibut?
I don't know why they released it. Nor do you. And presenting your opinion as fact doesn't change the fact that it's just an opinion.
Personally, I find your theory to be the least likely and most implausible. I believe it's more likely these recent tapes -- three in all from Zawahiri, dating back to September -- were released for the purpose of triggering a large-scale attack. Just as the last three series' of Zawahiri recordered messages were... and did.
Just my opinion. We'll find out soon enough.