My best guess would be a silly error that doesn't get displayed due to the threading. When I looked back over my coding I noticed something,
Run them all and then rejoin the threads
This line should have been a comment but it's not commented out so it is failing there.
Now I did notice that it appears to have issues running all of the different test cases for some odd reason. Threading can be extremely complex and honestly, SoapUI does not handle it that well. For scenarios like this I would personally recommend using Java to run SoapUI project files or some external source.
