That is truly sad, because despite your technical knowledge or not being a good fit for the company, the majority of recruiters forget that is all about people and all people deserve respect. As a developer you must have responsible with the people using your tool or product, the same is valid for recruiters: Is part of the job.
If you have time to interview a person, at least give some feedback, is good for the moral.
IMO this is one of the main reason of the impostor syndrome, there is a plenty of people who faces every day. Is even worse when you know you was very good on a technical test, but maybe you was a bit nervous or was bad in a spoken conversation, feedback is crucial to know where you need to improve and put some effort to become a better person in the future. (especially for people who doesn't have english as a main language)