User blog comment:Kirkburn/Technical Update: October 26, 2015/@comment-8014223-20151027162933/@comment-126761-20151027164824

Once you get close to that number, it severely slows down both Wikia and visitor browsers. This is not a perfect solution, but it is necessary to stop pages from grinding to a halt.

We recommend starting a new/successor thread every now and then, to avoid this issue.