Probably because there isn't anything. They won't say that though, because as long as they are still "investigating" they can use that to support getting future warrants etc. That is a common tactic among LE, when they know that evidence collected isnt relevant, they won't take that last step to show that and they definitely won't say that. They are just fine with letting someone hang in the air with an unresolved accusation against them.
I doubt there is anything to the *advertiser censored* allegations, after near a year they would have laid charges by now if there was. It is not that hard, there are about 2 or 3 computers in all, with a couple of external memory storage devices - how long can that take to analyse? The people who do this know what they are looking for, if there is anything significant they would find it pretty quickly. In fact, we know that whatever is there is minor because Toombs has commented on that, the first thing he said they had to determine was if it was spam, and then secondly who accessed it (which they are not going to be able to do). But, if they are considering spam as their first question, then it means that we are talking about very few images here.