There is a legal framework for interviews (e.g: EEO).

Probably they didn't like the candidate and they dismissed that person through a question they weren't expected to answer.

If someone was making a habit of asking impossible questions to members of a protected class and not to others I very much doubt that would be legal.

What does that entail? I thought the US was not as strict on law for workers / interviews.

Dismissing someone using an objective/concrete criteria such as a failed programming test is not problematic.

On the other hand, if you dismiss someone because "is not a cultural fit" or some other subjective reason, the person can sue you, accuse you of discrimination and challenge you to prove your point over a legal mine field.

This point is over-parroted. Anybody can sue (almost) anybody else over (almost) anything in this country. A butthurt applicant is not going to be dissuaded from suing you, if so inclined, just because you gave them an "objective" reason.

Most companies avoid that by not giving candidates a reason why they were not hired.

Well, if you did relatively fine they might still contact you in the future for other positions.

I can't tell if you're being facetious or if you're really that naive.

No company that I have worked for has ever said, "You know what? Let's look at the resumes of previous applicants, call them up, and see if they are still looking for new jobs." Every vacant position is always filled by direct, active applicants. Even backchannel applicants have to send a fresh copy of their resume to someone, so that it can be added to the applicant tracking system.

Tech resumes have a short shelf life. If the person is any good, and actively seeking to change employers, they will already have a new job by the time you have an opening for them. And if they are constantly doing a low-key, back-burner search, just to stay tuned-in, they will probably apply again to whatever you advertise, if they are still interested in your company.

The only companies that will keep your resume forever and call you back later are recruiters.

It may be that I have never been considered good enough to get hired, but not quite as good as the people they chose to hire on the first round, but for most companies, I either get an offer or I never hear from them again. Those still willing to communicate after a no-offer have never contacted me again regarding another open position. I admit there may be a theoretical nonzero probability of this occurring, but it has a lot of zeros between the decimal point and any other digit.

I'll offer a counter amnecdote: I submitted a friend's resume, he was interviewed and my boss liked him, but his boss didn't (I don't know about other feedback). Some time later, we had a new opening with some urgency and my boss asked me to see if he'd like to interview again; he was hired after that round (boss's boss did not interview him)

Many of the usual hiring practices can be bypassed if you already know someone at the company.

I had a company call me up years later based on an old resume. I turned them down, but mainly because I only applied to them because I was desperate (don't like the company) and the job they were offering sounded pretty lame.

I can't imagine it's a very successful tactic, and it probably only happens when they're desperate.

I'll ignore the insults and proceed to refute your point.

I am regularly contacted by recruiters from companies where I've interviewed successfully (with offers) and unsuccessfully (no offer).

They do it because it's cost efficient.

The book "Cracking the coding interview" also speaks about this in the early chapters.

No insult was intended. I intended to disparage the hiring processes of the companies I have previously encountered. Your experience appears to have set different expectations than mine. Perhaps it is a regional difference?

I work mainly with companies with a significant physical presence in the US Midwest and near-South. The furthest west I have ever interviewed was in Denver.

A significant number of the companies I have interviewed with lack even the ability to respond to a follow-up message the day after an interview, so never mind contacting someone months later.

And anyway a generic reason is "we decided to move forward with another candidate."

Ah right, in NL where I did most interviewing you are not allowed to ask a woman if she is or plans to get pregnant for instance. Not exactly a subjective reason, but I think akin to what you are saying.