Next time you need surgery give me a call. I don't have any relevant qualifications; I have no training; I don't have a professional registration; I don't have insurance; but yeah sure I can watch a few Youtube videos and give it a go.
I've received enough terrible medical and dental care from various "trained" and "registered" practitioners to value referrals much more than any credential or certification.
If you yourself truly believe that a professional registration is satisfactory, then I trust you practice what you preach by never researching doctor reviews. To do so would invalidate your argument.
Your experience with healthcare might be different, but my own experience in the US has been this: I rarely see doctors that have later contacted me to see how the treatment they prescribed was working. Nearly every other service or product I purchase entreats me with a satisfaction survey at some point. I've asked myself: why don't doctors care about my outcome?
I have concluded that while I am the one with the sick body and paying money to fix myself, I am not the only customer. The regulatory agencies, credentialing schools, special interest groups, pharmaceutical companies, and healthcare unions are too.