The creators sold the rights years ago, than sold the rights for more money for spin off characters like superboy then went to court and settled for a more and wrote a letter saying they formally give up all rights.

They have no case regardless if the country but because the legal system takes time, especially with foreign law involved so they wait till the last minute to try to force a settlement for something they have been payed for 3 times already. So your right its all about timing of threatening the moive to get a pay out. But all that will happen is the fans will suffer