Some very good threads have been closed for not much reason at all. No examples, just an observation.
The fact is that it's often the case that a thread is locked because things got out of hand, a staff member had to do cleanup (deletions and edits which aren't typically visible to the general membership) and then decided that the prudent thing was to close it to prevent a repeat performance.
What I'm saying is that while sometimes it might seem that there's "not much reason at all", the members often don't have enough information to make that determination with any reasonable level of accuracy.
Members with SPECIFIC examples of threads they believe shouldn't have been locked or should be reopened, should please contact the staff member who locked the thread via PM.