In an interview with Lee he said that he didn't chose the scenes he would depict but, in consultation with the publisher he found out where the plates would be placed in the book by the printers & depicted what would be on the opposite page. This meant that some of the scenes he might have chosen to depict weren't available.
I'm interested in Bb's theory - & it could be a very interesting subject to explore - though it might tell us more about the artists than about Tolkien's work. I've linked to my favourite Tolkien illustrations
before, but as to why they're my favourites - who knows....