Nokia ostensibly wanted to combine the cases at the ITC so that they could remain involved in a process that might impact them severely. However, I believe that real reason was that they had planned all along to get the joined proceedings stayed based on their claim of right to arbitration. They didn't believe that the ALJ would separate the cases.
Now that the cases have been separated, they wish to avoid coming back to the ITC and suffer the wrath of the ALJ. They now prefer to monitor the development of the Samsung proceedings and get a reading of the outcome and rush to settle before being called back to the ITC.