Geometry.
As you can see in your second example:
the position of the jib sheet can be pulled in by a set of barber in-hauls. Theoretically, that would allow you to put the tracks on the side deck, so that you get the maximum off-center distance for sheeting the jib (say downwind). For upwind, you'd correct that again with an in-haul. (Practically you may not need it, or you'd want to use a whisker pole anyway).
However, you need to not only look at the placement of your fairleads but also to where you want to place your cleats.
In your first example
we don't see where the jib sheets are cleated. In the top picture above, however, you see that they are lead through an eye to keep them parallel to the thwart - presumably for a more positive cleating. With blocks on the deck, you may not be able to get good cleating geometry.
Finally, wouldn't you force your crew to sit further back with the on-deck tracks? That would matter if you're interested in getting good balance. If, on the other hand, you are interested in having an unobstructed back-rest, then that's a clear advantage for the tracks on deck.
That's what I could come up with.
