I'm a bit late to this thread, but it looks like several factors are responsible for causing his attempt to fail (of course, I don't know all the details so this just my inference and assumption). First off, he may have attempted hastily (this is one of the things that one shouldn't do in an attempt is to act rashly without a plan or at least having time to prepare adequately!). That may well be one of the biggest factors for failure. Additionally, he may have used an inadequate round (yes, while birdshot and small pellets can still kill, they are less reliable and certain compared to buckshot or slugs). Finally, it may also be possible that despite hitting the head, he may have just missed the most vital spots (brainstem) and/or got medical attention before either drowning in his own blood, exsanguinating (bleeding out), and/or dying of trauma itself.
I do want to say that while firearms isn't a 100% guaranteed method (especially for people who didn't do proper research, homework, or preparation), it is still FAR more reliable than a lot of methods, albeit messy and barbaric, it will still be a method of my choice since I have reasonable expectation of success compared to many other methods. I trust the science and knowledge of firearms and am confident on it's success rate.
Last but not least, after having survived his attempt, he then becomes more pro-life and decides to spew pro-life spiel (no offense, but that's just not acceptable). I suppose if he was pressured by society (as well as people in his life) to preach the (pro-lifers') choir, then that would be understandable, but him projecting his own fear of death and pain into anti-choice and prohibition sentiments is just not acceptable.