I think the default of only recent threads reduces server load. The query to gather the total 'from the beginning' and paginate the results can be a lot slower and create a lot of server load, especially when there are search engine bots scraping through the site as fast as possible. You'll notice that even stats about post recency and whether or not you have viewed threads are calculated and provided to you asynchronously after the basic information is loaded. I think the website designer is trying to reduce server overload events by using conservative defaults.