The general rule is that threads are locked when they reach 50 posts in length. Members are always welcome to start a new thread with the same title plus Part II if they wish to continue the discussion. Long threads, over 3 pages, become difficult to manage, therefore the length restriction.
There are other reasons threads might be locked. If members flame one another, repeatedly post comments that break the rules, or discuss illegal activities, a thread might be locked or even deleted.
Only the administrator who owns this site can lock a thread. I don't know why the thread you are referring to was locked.
Moderator Crohn's Disease Forum
CD, Ankylosing Spondylitis, lupus, small fiber peripheral neuropathy, avascular necrosis, peripheral artery disease, degenerative disc disease, and a host of other medical problems.