I get it that giving feedback can expose a company to lawsuits and takes a lot of time, now, what's the excuse for not even informing the candidate of the rejection? many companies simply stop communicating.
These teams tend to grow fast and hire of a lot of junior people - that lack of experience combined with pressure and a huge volume of interviews(at a fast growing firm) results in a lot of inconsistent communication. When a sourcer/recruiter is dealing with 5-10 interviews a day with 80% of them not making the cut, sometimes they make the decision to prioritize building pipeline over closing the loop properly with people. And sometimes people just have poor time management abilities and let things get lost in the shuffle.