Those locked threads are the old threads, recovered from the previous Space,com forums called Uplink, which was closed 10 years ago. It appears that the Administrators want to start anew with fresh new topics and new threads by new (and returning) members. Those old threads are probably kept for reference, like a Reference Library. Most subjects and issues were debated in great detail on Uplink in those threads, by many very well informed members. You may find useful information there for most of your questions or interests.
The search function on the Forum List main page is labeled “Have a question? Our experts have answers.” That title may be a bit misleading. It will actually take you to a list of links to all of the old threads, in reverse chronological order, that include the topic for which you are searching. The search options there are obvious.
That is just my opinion. Moderators may have a better or more correct answer.