There's a longer rant out there but here's the short version:
It's simple and more importantly, for most people it doesn't fucking matter.
Getting to the gym and doing anything will have a profound effect on 99% of beginners. So why not go with something that's simple, is endorsed by someone who is well-respected and has plenty of anecdotal evidence of its effectiveness (since in the bodybuilding game, for the most part anecdotal and empirical evidence is as good as it's going to get)?
There really shouldn't be a need for thread after thread and page after page explaining why it works. But people need to be told what to do, and they need to "believe", so to speak, in what their doing. The most important muscle in the gym, by FAR, is your brain. If you're 100% behind your workout routine, you'll have a much better workout, will be more dedicated, and will see better results than if you have doubts about its validity (everything else "physical" being equal). Which is too bad, because for the vast majority of people, they're ALL valid, and picking one versus the other isn't going to make a noticeable difference (or at least not enough of a difference to make up for the mental energy and anxiety spent worrying about it).
So no, we're not all Rippetoe shareholders. It's just a very simple routine that is very likely to be effective, and it's supported by a well-respected person. All the rest of it is just crap to get people in the right frame of mind when they lift.