They did try to localize FFII, but abandoned it not long after for various reasons. Like WKPVII mentioned, III got looked over because of the arrival of the SNES, but there are also some technical issues as well. The game literally filled every part of the cartridge so remakes would actually involve redoing the game in it's entirety. They started on the Wonderswan but by then, ran into other technical issues (rumor was upgrading to posh 16-bit graphics once again made the game too big to fit on the WS cartridge) and scrapped the project. Origins, was basically a port of the Wonder Swan entries which is how they finally got released. After that, III just stayed in limbo. I heard rumors they were going to try and remake the game for the GBA but there was bad blood between Sakaguchi and the CEO of Nintendo at the time so no ports came out until after Sakaguchi left the company and I guess SE felt since the GBA was a mini-SNES, it would be better to skip III and just port the SNES entries cause it wouldn't involve remaking the games from almost scratch.

Finally, SE decided to port the game to the DS and the move to 3D justified actually doing a full remake. Unless they do a PSP 2D remake or Nintendo and SE stop being stupid and just translate the original and release it on Virtual Console (and whatever the Wii U is going to have) we'll probably never see a 2D version of FFIII in the West. SE dragging it's feet has also made it so the game doesn't have the same nostalgia factor outside of Japan either, so it would be harder to justify making a 2D remake and releasing it outside of Japan, cause sales wouldn't be guaranteed like all the other 2D entries that have been released (often multiple times) in America and the PAL regions. Course there is always emulation.