Unfortunately, I'm not sure I can explain it.
"Beach books" actually rely heavily on this tendency, of the reader to fill in the story around the framework that the writer provides. It's clever because it's not very much work for either writer or reader; there is no revelation, only the fulfilled expectation.
Which is satisfying to a reader who likes that particular story-framework, because he can plug in the details he likes best.
Something like a caper movie makes use of this--it allows the viewer's assumptions to function as part of the misdirection, while some sleight of hand is going on under the table.
The thing is, some readers only want a particular species of novel, or they want a book to be other than it sets out to be, so they will judge it against the book in their heads rather than on its own merits.
If I want a tuna sandwich and you give me egg salad, it doesn't matter how good the egg salad is. I didn't get my fucking tuna, and I am gonna be pissed.
OTOH, if you can convince me I really wanted egg salad in the first place, and just didn't realize it....
..congratulations; you have subverted the genre.