Forums Question

Can someone explain how it is that an active Thread in a (until yesterday) very active support forum, started back in mid July/2014 with replies posted in it the past 2 days (Sept/16 & Sept/17 2014) ends up buried on the 5th page of Forum threads, and well below/after nearly 100 less recent postings in other threads? If there's logic or reason for this please explain it...  If there's a setting that corrects it please elaborate as to how to do it.