There can be many reasons. First, we're assuming the anemone is bleached because of something the LFS did or didn't do. That may not be the case. Unlike when we order something from Live Aquaria (or whatever online store you may use), a fish store generally can't return an animal to its distributor if it arrives sick or even dead. Now, hopefully an honest person would either not try to sell that sick animal or at least be up front about it, but that's not always the case.
We also sometimes assume that the owner or the workers at an LFS are knowlegeable about the care of the animals they're selling. Sadly this is often not really the case. I have met some who really are quite knowledgeable, some whose knowledge is quite outdated (they're too busy trying to run a business to study up on the latest and greatest), and some who really have no idea what they're doing.
That's why it's so important for us to know how to identify a sick animal. Regardless of whether or not the LFS owner/worker should know or do better, in the end, we're the ones who will have to live with the consequences if whe haven't done our homework. . .and we've all been there and done that.