The issue isn't just with the MJ estate. it's also with the music producers at the time who worked with MJ as well, as well as the fact that the music that was taken out that MJ worked on, was possibly repurposed into MJs other songs, either by MJ himself (since he did some compositions on his own songs as well), or his music producer. It's a downright mess for SEGA to sort out. It's actually kind of interesting, it's probably also why Metal Gear Solid 2 and Metal Gear Solid 3 have not been re-released since last gen either, since the MGS Main Theme at the time has been found out to also be somebody else's work originally. Then there's the fact that Onimusha 1's OST had to be redone entirely because of the composer being a fraud. There's so much trouble with the legalities of these old games nowadays it seems like, since they used to get away with re-releasing these games more than they do now.