Their excuse? A combination of things that basically boils down to the fact the poor performance of the first two games in the series in the West mean translating the third one isn't worth the time/effort.
And it's an excuse that just doesn't cut it. So the first game lost money? That's because you spent AAA money on a niche import title. So the second game bombed? That's what happens when you release a PS2 game in 2008.
This doesn't need to be localised into 7 European languages. English will do. Even if it's only released in the US, people from Canada, the UK, Ireland, Australia, New Zealand, South Africa and Singapore can import it, not to mention those elsewhere with the English skills to get by.
Come on, Sega. If you could be bothered releasing the game in Korea, you can do the same for the West. It's only fair.