I wonder if JRR Tolkien every got grief for the 17 year gap between The Hobbit & Lord of the Rings? Probably not
Actually... yes, he did. Quite a bit, as a matter of fact. And it was the anticipation for "a new Hobbit" which played a large part in nothing of what became The Silmarillion being published during his lifetime, as that work didn't interest the publishers, while a sequel to
The Hobbit did....
As for the "implicit contract" thing... well, frankly, that's utter nonsense. Understandable nonsense, mind you, but nonsense nonetheless. As a reader myself, I feel sad and disappointed when such things happen -- I'll always regret, for instance, that Gordy Dickson never finished his Childe Cycle... especially as I'd been looking forward to reading the entire thing as a unit since I was about fourteen (that's nearly 38 years now). And I've always wanted to read the other two (never written) books in Avram Davidson's proposed trilogy which began with
The Island Under the Earth....
But
no one has a right to expect a writer to write to suit them. They have a right not to buy that writer's work if they don't like whatever else the writer does; but writing, as a creative endeavor, cannot be held to such a contract of continuing stories of the same type (let alone the same series) in the same way as someone with a "day job" can be held to their normal duties, without the quality suffering greatly from it -- unless the writer him-or-herself feels the continued inspiration for that particular type of tale. Creativity such as this can seldom be governed in that way; it relies too much on factors beyond our conscious control; and, if you want something that's actually worth reading, you just have to be patient and hope that the writer's "afflatus" continues in that vein. Otherwise, you're in for a world of frustration, either by being irked at nothing coming out, or having what does come out fall well below that writer's standard, let alone their best.
