I do know the reason for the repetitive maps. Beware, for lore lies ahead. The battle of the Twilight Gap is where the Iron Lords were made. This was a defense against the fallen, who had launched a massive attack there. This is also where Saint 14 and Osiris became quite famous. This is why Twilight gap is featured. Osiris later went to Mercury, thus why Mercury is repeated. The cathedral of dusk and other dreadnaught maps are the cause of what I believe revolves around destiny's original story, in which the warmind Rasputin was abducted and held on the dreadnaught in the form of an Exo, thus the photo of the bloodied exo in concept art. This is a possible reason for those maps, as well as a little bit of stuff to mix around. Exodus Blue may appear as well, as a tie to the attack on twilight gap. Banner fall may just appear because Bungie had an extra map lying around, or, this was a previous area of the tower, that was left behind either from the disgrace of Osiris, or possibly housing the great guardian Saint 14, and was left behind as a memorial, and later turned into a crucible arena by Shaxx, another veteran of Twilight Gap. TL;DR: Backstory.