Sometimes, even Bear Spray is not as useful as it is presented, even though it seems it "finally" worked in the situation described in the article.
https://www.cdapress.com/local_news/...ana_wilderness
One 'takeaway" is whether or not, regardless of what you use, can you deploy your defense quickly & effectively when it is needed.
Folks can draw their own conclusions from what they can get informed about, in regard to wildlife attacking humans.
I, personally, am gonna the do the best I can, regardless of what I have, be it a rock, club, a sharp stick/spear, a firearm or a howitzer, etc, or even my own physical abilities to try to prevent more issues.. That is gonna depend on , "WHAT I have with me." & "What is attacking me.".
If all I have is a 9mm, for man or beast, then that is what I have & I will use it. If I can prepare for "worst case scenario", then I will choose something more appropriate, IMO, to deal with such issues.
Here is a great time to offer the acronym/phrase,"YMMV", or "Your MIleage May Vary". Since everyone has different abilities in handling issues & what is available for defense.
The, OP, asked, "Why is 9mm great for people & not bears", and personally, I think the answer has already been answered in these last 3 pages. If not, then may I suggest someone go out & do some actual testing and get back with us on the results... Otherwise, like the old commercial about the Owl & the Tootsie pop, with how many licks does it take to finish one... And the answer provided then...
" The World may never know..."