Ask HN: Do your companies reply to rejected candidates?

I'm applying for software engineering positions right now and in the past month or so have interviewed with many companies, from small startups to massive MNCs.

One surprising aspect has been that some companies' recruiting departments have been non-communicative after the interview. Like, no reply, even after I've sent a reminder/check-up email (I'll wait a bit more than a week before sending such an email).

What's going on here? Is it actually a thing for companies to not reply to rejected candidates? That seems really rude. Again, I'm not talking about cases where I blindly sent in a resume; this is after one or more technical rounds.

Maybe candidates just slip through the cracks? Still, it seems bizarre that a recruiter wouldn't take 10 seconds to send a generic rejection email after their engineers have taken multiple hours of their time to interview me.

To be clear: I'm not trying to complain (too much); my job search has been successful. I'm just trying to figure out if this is standard practice, what it means, and how to react in the future when it happens.