One good reason why the US and EU POL had no IME support was the fact it was originally designed for being compatible with Windows 98. I don't think the current version of POL even boots properly on Windows 98.

Because of differences on the Windows9x software, adding IME support to POL would cause it to only work on NT based OSes as Windows 2000 or newer.

Now, regarding the PS2 version, it uses ATOK, which is a copyrighted piece of software (JustSystems, an Japanese word processor developer company owns it) and indeed they would have to pay JustSystems royalties for it.

But hey now Windows 98 is GONE and they could update the international versions of POL to make it work with IME.

As a side note IME works just fine with Final Fantasy XIV regardless of the language the game is setup as.