Just because behavior is common doesn't mean it's acceptable or should be tolerated. Companies expect candidates to be professional and can't send a simple email? What else would they be cutting corners on?
How do you "not tolerate" it? Send them a nasty email? Create a 'wall of shame'?
One thing I've heard from larger companies is they often do not say anything because almost anything can be construed in to a lawsuit. I think this is a bit of a copout, and I think in most cases, it's just easier to do nothing, but the lawsuit thing probably isn't a total non-issue for some companies either.
"Thank you for your time and interest. We were faced with a tough choice with a lot of candidates, and we ultimately went with another candidate for this position" seems as inoffensive and bland as could be - why these aren't sent out it, I don't know.
I wonder if any companies know/care how much this kind of behavior negatively impacts people's perception of them.