IME, not only are they quite hardy (I kept mine under 4-40watt NO fluorescents for a long time) they also seem to ship very well (of the ~10 I have seen at wholesalers, I have yet to see one in bad shape). When I got my first 2, the wholesale price was $24.

That was before people started looking for them and wanting them.
I think the biggest reason you don't see them often is that they grow quite fast in nature and finding one less than 2 feet across is difficult. It also might be difficult to get them off the rocks because they like to bury their foot in a crevice like a BTA.
I bought a silver dollar sized one from Blue Zoo about a year ago for $40. They had 3 of them for quite a while before they were able to sell them. They are popular on this web site but in the general population of salt water hobbyists, I don't imagine they sell very well compared to colored haddoni.