Don't know how long you have been in the hobby, but there are lots of things that seem 'intuitively obvious' today that were not always so. Places like RC, frankly, make it quite a lot easier now to adopt best practices than when I started up my first reef tank in 1988 and was largely 'winging it'. It's only been for about the last 10 years that I have employed strict quarantine procedures for fish - prior to that there really was no consensus that it was a worthwhile thing to do. Heck, even today there are some experienced reefers who eschew the practice.
I started about 10 years ago, so perhaps that explains it. Although I am also in England, which may well be another factor. It's very rare I have come across someone who doesn't quarantine. Actually that's not true, I have met quite a few people who take up the hobby because a marine tank is pretty but they on't really bother much about understanding how to care for it properly. These people have never stuck with it for long, most less than a year TBH.