Because the default tends to be to say nothing, frequently if you just ask directly for feedback may get it. Its a bit of a back door to the policy.
When I worked for "MegaCorp" we didn't give any feedback voluntarily but if a candidate asked me directly I would let them know. I frequently hired junior engineers* and felt almost a responsibility to give them some input, particularly if their issue was technical. If they were just an ass, I'd likely stick to the company line and not say anything.
* I found most senior engineers are pretty well aware of their deficiencies and almost never would ask for feedback.
When I worked for "MegaCorp" we didn't give any feedback voluntarily but if a candidate asked me directly I would let them know. I frequently hired junior engineers* and felt almost a responsibility to give them some input, particularly if their issue was technical. If they were just an ass, I'd likely stick to the company line and not say anything.
* I found most senior engineers are pretty well aware of their deficiencies and almost never would ask for feedback.