My guess for the first gates not having dual-bridges: because they stick out so far, the footprint of an aircraft requiring two bridges would be too large. Odd though, that those first two gates stick out so far; I immediately thought of the Victor Pier (i.e. poor planning, long tubes snacking about, endless walking...).

I would have thought the dual bridges would have allowed access to upper- as well as lower-decks? Assuming these were designed with the A380 in mind, of course. But I don't understand how these gates could service two doors. If anyone knows about the dual-bridge gates at AMS, the second bridge usually extends over the wing to a door further back.