I wonder why this is seen as being an effective way of mitigating the risk of discrimination lawsuits? At some point, whether you explicitly tell them or not, the candidate knows they didn't get the job.
I can see where it might be problematic to go into reasons why they didn't get the job, but I'm having a hard time seeing what risks a simple notice informing them they didn't get it causes?
It's quite simple: Wording. Somebody might have gotten sloppy writing requirements for the new position, or HR may have misunderstood the requirements.
This may be enough to give the rejected applicant ammunition for a law suit. I've been to several interviews where I've had to dig out that what they say they're looking for doesn't match the position they actually want to fill.
I'm a straight, white male in my thirties, so discrimination is far from my mind. Other people may form different ideas, though..
Without a rejection letter you'd have to prove in court that you have been rejected in the first place. I imagine few judges will take such a case, otherwise people would be suing every single company for "rejecting" them by not actively recruiting them.
On the other hand, going silent after there already has been some communication established does not seem to be smart. But I am not a lawyer and there could be some sense in that too.