There's a difference between wishing and doing. They wish there was a way to give feedback while avoiding the trouble you're pointing out. Since there's not, they're just left wishing instead of doing.

Hiring managers work in a very human field. They often run into the same issues with candidates, and wish that they could just give a bit of human input, to help someone else. The candidate might not be a good fit for that job, but if he/she is unknowingly self-sabotaging in interviews, it would be great to be able to point that out. Since the potential trouble outweighs the benefits, they're left only wishing.