The cleaner wrasse is not all that tough to keep in a tank. They do have a higher loss rate than yellow tangs and algae blennies, but keeping one in your tank is not as much of an accomplishment as it was 10 years ago.
The issue with these fish is their value to the other animals on the natural reefs. If they're over collected, they aren't there to help rid fish of parasites, which is their job. Without them, or I guess, without enough of them on the reefs, disease can become much more prevalent and then fish mortality and so on.
The combination of their (still) fairly high loss rate and value in nature makes this a fish that probably shouldn't be available, or at least not as available as it is in the hobby.
That said, a LOT of people have one in their tank, I have one in mine.