One of the options there is "Show threads from the.." (date range), which has a fairly low value... simply setting it to a higher value will show you more threads (currently up to 10057 threads for this forum).
The Admins decided to set the limit fairly low because it saves server resources, and most people don't care about seeing what was posted 3 months ago... if they want to view old threads, they are probably looking for something specific, in which case a search is a much better option.