Actually thinking about it, whatsapp can play a role. They say they want to find ways to stop the spread of such videos - we all know that's nearly impossible on the internet as a whole, but in a world where for most people the internet might be primarily whatsapp or similar there is an obvious way: check files against a database of hashes for 'prohibited' files. Same way Dropbox checks for copyright violations, YouTube for copyrighted video and sound or Microsoft's child porn checker.
So you could say if the company would want to address this issue, which is largely occurring on and through its technology, it could do so. You wouldn't be able to stop initial spreas, but if people get the chance to report the spread might be stopped quite early exactly because it's such a conservative society.
Not saying that's the ultimate solution(or even a desirable one) and there are plenty of caveats - but if companies wanted to address the issue they could at least try, so whatsapp/fb is certainly not 100℅ off the hook. That they haven't made any attempt to provide mechanisms to stop this kind of thing was their choice.
Or is there something that just wasn't active here? Eg does whatsapp block child porn distribution or copyrighted materials? Fb is pretty strict on that kind of stuff so I'd be surprised if there's really no mechanism yet.