I think there is some fear is in responding negatively due to the vagaries of employment law, where you are giving people the opportunity to challenge you for not selecting you for the "wrong" reason. This is why most responses should be just,"we have not decided to bring you on at this time". I always like to keep a pipeline of potential candidates warm, contacting them at least once per month, so giving no feedback whatsoever seems like a bad strategy for anyone you might ever want to hire.

However, you have to just start to imagine all of the things that happen on the other side of the curtain. The hiring manager moves to another project or hadn't been assigned when they started interviewing, the recruiter changes or their contract ends, the project funding gets delayed, the technology choice changes, they didn't know what kind of person they wanted, etc. In larger companies, you need a lot of coordination so that you don't lose a good candidate due to their not being a fit on the project that got to them first.

I would never expect a response other than "resume received" from an online submission, but, once you speak with someone, a status update of some kind, even if it is a "no decision has been made" makes sense.