We must be talking about two different screens. @shadowfax described it accurately - - The threads are usually revived by people who surf in and register and aren’t starting from the forum’s main page. the discussions on community.cartalk.com are in reverse chronological order. Sometimes spam posts that get removed leave the old discussions bumped up in the order, but those are few.
Suggested topics (when they’re at the bottom of a topic you’re reading) are in reverse chronological order. There isn’t much rhyme or reason that I can detect, but it’s mostly old discussions I participated in, and aren’t the most recent overall discussions for the whole forum.
But to return to my original point: please do not jump on new people to blame them for reviving an old thread. It’s not their fault, but it’s also not a design issue, either.