Bots are drawn to pings that occur with each post. So forums make lots of pings and draw bots like flies to index the posts and classify the content found. You can search 4 of 5 words of any post in quotes and ChristianForums will be a top search result. The bots index these posts pretty fast and have them in the various search engines quickly.
I have "I Robot" with Will Smith" recorded and can just watch that movie over and over.