That sounds a touch snarky toodeep - it could be that his publisher had him going elsewhere or real life
intervened.
I'm not sure why that sounds snarky when you then turn around and agree with me. I assume that publishers do a complicated dance when determining where there will be signings, to maximize the return on the authors time and the rewards to his fan base in such a way that they feel it will help the sales the most. It is possible that they did not see an expected bump in sales or news articles or something of that nature from the Ann Arbor book signing when they came out for Changes, and thus they did not come out again. Saying that the publisher chose another location based on historical results or calculated effects of his time investment, is saying that we didn't rate another visit. That's not a diss on him or his publisher, but is what I assume. I can only hope that something changes this calculation for a future book, or that our fair area comes up again in the cosmic list of areas to visit. I don't really care why, I just hope he comes.
Real life interfering is a possibility as well, as always, which I did not address in my post because I generally don't attempt to theorize about personal lives; while I feel business decisions are fair game.