Hi Alan: I have no idea why the publishers would not also publish a PB edition, given that most--but not all--of the other books on the first and second page have PB editions. Perhaps they are waiting to gauge potential PB sales based on some formula, but that's just a guess. A PB edition may be forthcoming as I noticed a time lag of several months (and in some cases years) between the date of the HB and PB for several of the titles.