What you've got there are two long platforms (plus one short to the upper right). I believe choose signs, like choose signals, select platforms, not individual tiles. The reason for this is that vehicles do not necessarily fit in a single tile. Although multi-tile road vehicles are rare, they do exist. There is also the fact that vehicles stopping on stops placed along a road like that hinders other traffic. The logic for overtaking may possible get around that if certain criteria are met (the same for overtaking in any situation I believe).
It is also possibly that such a layout would not be very efficient even if it did work, if the traffic is high enough to warrant so many tiles to stop on in the first place. In such a big city, I would not expect that buses need to wait for a load.