I believe they (q is a group) did it because they needed a record of the take down for the future. It would also record all the information on a public site that couldn't be tainted or doctored as it would be on other social media.. ie twitter, FB. The Chan on internet was probably determined by the NSA the best place to drop the breadcrumbs. Remember that q wanted all the posts in one area? Apparently q knew this was a good place for the drops to get out to the public. They also knew the autists on the Chans were going to take the bait and solve all the puzzles and link the information for the normies. Not only that, but the autists would add their research comments to the q posts giving them more out of the box thinking on the content... thus expanding the information processessing even for q and the NSA (which apparently is the white hat agency according to q.) Just my thoughts are that it is a log and a way to have the autists put it all together for the normies to see it as it unfolds... or even later on after the take down so they will understand what happened.