Our feedback forms are supposed to go to the referee as well as the SADO, and I have tended to assume referees don't think it wise to be critical (well, not on paper, anyway). Or just lazy.
Standard RFU set up used by most Groups/Feds/Societies is that
Adviser Report goes to referee (& referee coach) as draft for discussion [used at higher levels only].
Published version goes to Referee (& Coach) plus Grading Chair or Secretary (and then to other members of grading committee - weekly, monthly or one big chunk) for Grading decisions evidence. Also goes to SADO (Society Advisers Development Officer) - who is often but not always Chair of of Grading too. SADO is interested in standard of reports, is de-brief and are interpretations correct, referee ddevelopment needs (feed back to Traning & Development Officer) and potential.
Adviser feedback forms are sent by referee only to SADO and are never shown to Advisers - referee anonimity is protected. These are used by SADO to ensure high advising standards are maintained - pre-match contact, arrival in good time for comms etc, understanding of match shown, clear structured de-brief, and report reflects de-brief.
At Federation and Group level the Adviser Feedback form is mandatory for all referees to complete.