Honestly? Pretty smart move by them. Japan's major export is its culture. Nowadays almost everyone enjoy manga and anime and by extension, they adore Japan. That kind of soft power can be very useful. By allowing unlimited access to their cultural outputs, including copyrighted materials, they can influence the AI and further boost their reach.

You can sort of see this in Stable Diffusion and music models like Suno. Lots of creations are basically Japanese art.