For me personally, one of the biggest reasons why I wouldn't have looked is because there is a perception that the probability of things this dumb being missed means looking is surely a waste of time that could be billed hourly to paying clients. It's moments like these that really challenge those assumptions.
But I suppose the most likely possibility is that the Apple and GnuTLS bugs earlier this year made many groups begin a deeper look at trusted-but-not-really-well-reviewed code. OpenSSL fits that category, and with many (?) teams now combing it, discovery collisions during the window of time between "1st realization" and "released fix" are more likely.
Still, if doing a fresh & deep look at OpenSSL, and finding something of this magnitude: would a researcher race to both inform OpenSSL and deploy a fix ASAP, or would they instead, suspecting there's much more low-hanging-fruit, try to review further before disclosure and batch things up so the eventual shock/pain can be handled in one internet-wide emergency, not many?
Which is a roundabout way of asking: are we about to get a bunch of these trickled out as Mehta, Codenomicon, & others continue to work through the code, or did we just get this because that review process completed?