The Glock kB! issue has several contributing factors--there is not one single cause. The lead bullet/polygonal rifling issue is one, there are several others.
The problem with the nearly all of the contributing factors is that they're not "reliable" and that makes it hard for people to buy in. People want things to be black and white. They want an expert to tell them that if they shoot some specific number of bullets of a certain hardness down the bore that it will blow up the gun but if they limit themselves to some carefully defined number of bullets less than the dangerous amount that they will be safe.
It turns out that it's not anywhere near that simple. Small variances from one gun to another mean that one gun may tolerate a lot of relatively soft bullets while another apparently identical gun may start to have trouble with a much lower number of quite hard bullets.
Some other contributing factors of note (I'm not claiming this is a complete list):
Early in the .40S&W's career there was a batch of weak cases from a major manufacturer that resulted in a number of kB!s. That has been solved.
Case support issues--largely eliminated with the newer Glocks.
Bad ammunition, especially reloads. The shooter is understandably loathe to blame himself and tries to blame the gun. The only kB! I've been personally involved in was something of a mystery until the guy who kB!ed the gun left the scene and his friend told everyone that this was the shooter's first time reloading. This really has nothing to do with the gun, of course.
Out of battery firing. The Glock design, especially when badly worn and poorly maintained can develop the ability to fire out of battery. There are other limiting factors in the design that prevent this from being a major danger (as in the gun blows itself to pieces), but it can result in case failures. The typical result is a stinging hand for the shooter, the mag is ejected from the gun and sometimes the extractor goes on holiday.