The line is between saying something brief and saying nothing.
Somehow, it has become standard to say absolutely nothing instead of telling people a simple no.
I've even had situations where people said they wanted to keep talking to me, and then went completely silent.
The sad truth of the situation is that all the incentives for a company point in the direction of giving no feedback at all. This isn’t because hiring managers are sociopaths.
It's just common decency. "Sorry, we're not continuing" is not going to get you sued.
The time to send the "Sorry, not continuing" email is as soon as the company has decided that, and if that really is 1-2 months later, you may as well have just ghosted the candidate.
This happened to one of my bosses. As a result, I've never attempted it.
Except once, a candidate realized at the end of a technical screen they had done poorly and demanded feedback. I gave an initial bit (shouldn't have, my mistake) and instantly turned it around on me.
Hell if companies would even do that - I've spent a lot of time (7+ hours) interviewing with some known companies including meeting with the VP of engineering and then they just stop messaging and ghost you (looking at you Glassdoor..)
For example, in an interview once I got the typical "design Twitter" whiteboarding question, and it's going fine, until the topic of databases and storage comes up.
I ask "do we want consistency or availability here?"
The interviewer says that he wants both. To which I say "umm, ok, but I thought you said you wanted this to be distributed?", and he said yeah that's what he wants.
So I have to push back and say "well I mean, we all want that, but I'm pretty sure you can't have stuff be distributed or partitionable while also having availability and consistent."
We go back and forth for about another minute (or course eating away at my interview time), until I eventually pull out my phone and pull up the Wikipedia article for CAP theorem, to which the interviewer said that this is "different" somehow. I said "it's actually not different, but lets just use assume that there exists some kind of database X that gives us all these perks".
Now, in fairness to this particular company, they actually did move forward and gave me a (crappy) offer, so credit there, but I've had other interviews that went similarly and I'm declined. I've never done it, but I've sort of wanted to go onto LinkedIn and try and explain that their interview questions either need to change or they need to become better informed about the concepts that they're interviewing for. Not to change anything, not to convince anyone to suddenly give me an offer, but simply to prove my point.
A scary number of candidates did not take rejection well and tried to use my feedback against me. I had people trying to argue that my feedback was wrong, someone stalking me across social media and trying to argue everything there, and eventually someone who threatened to use my feedback as the basis for a discrimination lawsuit.
So now we’re back to simple “we’re proceeding with other candidates” feedback.
If we’re going to play the blame-game, then you have to see the full picture. Many candidates can be awful and even vengeful. Many people do not handle rejection well.