The posts are still here...you just have to set different parameters in the "Search" field. I search by date(s) sometimes.
But yeah, it's hard to find a particular old post or thread unless you've bookmarked it or copied it or you can remember a specific phrase or the name of the thread.
You know you can access all the threads you've started quite easily, right? I saw your first thread from 2013 just by going to "All threads started by zerothehero." The site only indexes the last 500, but you've only started 41 threads, so they're all there.