Important to note that this suit is not with respect to copyright violations. It’s the union suing about re-use without the musicians being paid “re-use” fees.
This action is a double-edged sword. On one hand, you have to applaud the AFM for making an effort on behalf of its members. On the other hand, some will argue that the AFM is only providing further incentive for scores to be recorded outside the US and / or with samples.
As far as the copyright issues are concerned, the scores were most likely done on a WFH basis and, as such, the property of the studios. In which case, they would generally be free to do what the wish with the music.