I’ve lost count of the number of jobs I’ve applied (and interviewed) for where I’ve just never heard from them again.
In fact on indeed there is often an update which states how long it will likely be before you hear back, and I’ve seen one or two which state “based on our experience, you’re unlikely to ever hear from this employer again.” 
TBH, if we were in the days of paper applications I could see how writing a letter to each applicant could be problematic especially if you have several of them.
But given everything is now done electronically, and there are generallly systems in place to acknowledge your application/invite to interview/confirm the interview time etc, I fail to see why there can’t also be something in place which generates a rejection email when the applicant is rejected on the system.
It would save a lot more angst when people are applying for jobs and just hoping that they will hear back about one of them, only for it to appear that their application has disappeared somewhere.
i interviewed for a job recently and have assumed I wasn’t successful. But it would at least be nice to have been told so I could ask for feedback.