He has been stringing his fans along for over a decade. It is rude and cruel. It would be like teasing a puppy with a treat but never giving it to them. For 10 years. That is what he has done. His editor disagrees with me [1] but makes an equally strong point.
I guess if grown adults are akin to puppies for you in this situation and the writer is cruel and rude for not writing another book then we see things too differently to agree in any meaningful way.
[1] https://i.redd.it/4g1jexk7i9e51.jpg