Anyone can start a thread there, and reply to their own thread.
To respond to someone else's thread, you must be a forum member of 5 years or more (veteran), or demonstrated to offer knowledgeable and safe advice in other areas of the forum.
We had problems in the past with people posting there with well meaning but dangerous advice, or berating people instead of helping them, or simply saying condolences which clog up the thread, making it difficult to find the advice.
While this change is not a perfect system, it has helped tremendously to ensure people are getting more accurate, safe information, and the thread is not clogged up with fluff.