I guess one possible explanation is that having a black box in your plane is not useful to you, only for other people after you die. Pushing for the idea requires accepting you are going to screw up and some people will think that your job is preventing the airplane from crashing in the first place. It's obviously useful in the long term from a societal perspective, not from a short-term and individual point of view.
Even then I don’t get why someone would object. But of course hindsight is 20/20 so that may be why. Having a black box in all aircraft would help me too, because other crashes are better understood. Then again I also do want my death to be maximally useful to others should I die, so that at least I don’t die completely in vain. I don’t want to live forever, but I don’t want my life to end abruptly and outside of my control either, and I have plenty of things I want to do still before I leave. So that may also be why I don’t understand that POV you suggested.
Also, if I was a pilot, I would appreciate the fact that the black box can potentially help my friends and family get closure, because if the black box survives then my friends and family can learn what happened that caused the crash.
I think pilot must have known that the information in the back box would provide them heaps of data on how to prevent crashes, to their benefits. My guess is that is was not opposed by average pilots, but by people in power above or around or among pilots, whose power would be undercut by any new idea.
