I use photo references as well. All the time. But my drawing background (and I'm sure yours) is drawing from observation. Heck even dadaists, who created the first photo collages, created something new from pre-existing photography.

I think when it comes to fanart it's a little less done. Probably more to do with the ratio of fanartists in fandom vs. writers.

I personally think this is a combination of not knowing any better and ignorance. However, after being told more than once that the artwork is fishy, I wonder if stubbornness is getting involved to. But I can't begin to think like someone else.