Nothing odd about it.
I started out with
'The beta forum is for tests that go on for a certain time and then finished. Once a test is over there's no need for the thread to be kept open.'
but then I remembered that the FE introduced an automatic lock for threads with no new posts for some time in order to reduce the chance for spammers to attack that way.
Dig into the past of this forum and all the threads are locked.