I was expected to prepare (in advance) a number of things including a technical presentation and detailed answers to a large number of questions, which took me several evenings and most of a weekend. I flew there on a monday for what was an exhausting full day of interviews before my return flight that evening. The recruiter phoned me the following day to say they were very impressed and would be making an offer, but there were some other people who wanted to meet me.
So a few days later I took another day off work to fly down for a second round of meetings. At the end of this second day I was told that the senior manager was abroad and they would finalise the offer when he returned.
I flew back home and waited a week or 10 days before emailing to hear how things were progressing. The recruiter responded "to recap, we are waiting for $manager to return before finalising the offer".
That was about 7 years ago, and it was the last thing I heard from them. I get that employers can't be bothered responding to every CV that crosses their desk, but this was a demanding process that cost me several days effort and 2 days salary. Maybe they lied when they said they liked me, I have no idea and don't really care. But I certainly didn't expect to be ghosted after all that.
A year or two later I had a new colleague who had been working there around the time of my interview, and I told him this story. His response? "You dodged a bullet".
It's probably at least 50% of my interviews. Roughly 1/4 of my interviews have any kind of follow up at all.
It doesn't hurt to tell people that someone else was hired. Closure is important to job seekers.
The only reason I called was because they stiffed my the reimbursement for travel expenses which they had agreed to pay for. The HR turnover was so high that everyone I had talked to before the interview was gone by the time I put in for the reimbursement.
Clearly things went your way if you didn't get the job in that environment.
Funny story about that, I'd set up a macro to fire off said email with one keypress. Finishing up a phone screen that went horribly, I thanked him for his time and all the other niceties, and pressed the key right as I was about to hang up.
"But wait! I have some questions for you, too!"
Cue the longest 5 minutes of my life.
After reading some of the comments here about candidates who want to debate the interviewer's decision, it seems to make sense.
Sometimes they'll dangle candidates if they're waiting to hear whether their first choice accepts, but even then it's rare not to communicate at all once you've done an on-site.