Professionally, I still hate it, but to some degree I understand it. Forgetting even the matter of additional business spent personalizing rejections, the truth is that most of the time the rejection will be taken personally, feelings will be hurt, and any feedback given won't be actionable anyway.
"Sorry, you look good on paper, but your solution to the challenge you was buggy, and you misunderstood the requirements. Go become a better developer."
"Sorry, your code was good, but you struggled to convey information to us. It appears you're a terrible communicator and that would cause problems on our team. Maybe some books on the topic would help, but I doubt it."
"Sorry, you aren't a good fit for our culture. You're abrasive and rude, and talked to the interviewer like you knew better than them. Quit being a narcissistic jerk."
If you're talking about being rejected at the application stage, IME it probably means you didn't follow the instructions completely, you don't actually meet the requirements (remember, it's probably HR or someone non-technical doing the first stage of rejections; they're just driving by checklist, so simple things sometimes get triggered here; if the requirements say "5 years JavaScript experience" and you list "5 years React experience" that might not make it through their filter), or your resume/application needs revising.