This is by design, because we believe that if it would not be anonymous, people would not share honestly their thoughts.
We made some experiments back then, without anonymity, and to give a simple example, someone who shared a bad day saw her manager comes to her, asking to explain why, but this was obviously not the right time for her. Then she ever said she had good days, in order to not be disturbed by her manager.
For us, anonymity is the best way to get genuine feedback, and it is the job of the manager to address the issue, even s.he does not know who raised it.
Manager is not an easy job.