perhaps a violation of trademark =)
perhaps they do think that *as long as* no one is selling and getting profits from their works. also in most cases, that's because they doesnt create anything new or fresh, just crap with artspeak imo. it is ('almost'

impossible to create 'clean' art without influences, but that doesnt mean it takes away the originality of the work. you can always claim someone's art to be from as deep as his parents dna, past lives etc. furthermore, we get more information/influences from one big newspaper than a ordinary human in medieval times get during his whole lifetime.
it's exploitation and raping of da vinci.
best artists forget the creations of past and create the visions by themselves imo.
-tomi