I think whats happening is this. Most of the Allied Navies have a reasonable quantity of warships already ingame, where as the Axis Navies are atm rather poorly numbered. So in light of this I think most of the shipwrites have geared their work to correcting the imbalance. Now I suspect thats as soon as this is achieved, we will see a trend to expand other navies be they Neutrals or Allied.
I can say with some authority that the Allied navies are being worked on behind the scenes, but not with the same fever as the Axis. Just give us some time and we will get there. After all this is not our day job.