Adaptation by Vague Recollection

[Zigûr]

I was talking to a friend about "The Hobbit" films today and he was asking me to remind him about what happens in Lake-Town in the film as opposed to the book. We talked about it for a bit, and I found myself thinking about how little resemblance Lake-Town in the second film has to the book.

Consider the following:
Book: The Dwarves openly announce themselves
Film: The Dwarves hide and enter the town in secret, with much climbing through toilets and so forth

Book: Many Lake Men are impressed or excited by the idea of the King Under the Mountain returning, and to curry favour the Master puts them up in comfort and style with gifts and servants
Film: The film switches focus to Bard and his family, and Bard's investigation into the truth of Thorin's claims, as well as his power struggle with the Master. Meanwhile, the Dwarves try to steal weapons from the town armoury (for some reason) and are caught; Thorin gives a big speech about gold to win their favour and the Master helps them for that reason; his motivations are comparable to the book

Book: With the help of the Lake Men, the Dwarves set off up the River Running for the Mountain
Film: The Dwarves set off alone, and some of them even stay behind

Apart from, perhaps, the Master's motivation, the entire sequence bears astonishingly little relation to the book. Now, the argument would be, of course, that the filmmakers told the story that they wanted to tell, and thus they changed it. That's reasonable enough.

Yet thinking about sequences like this, I can't help but feel like to an extent this is the product of a screenwriting conversation that goes like this:
"What happens after the Elvenking?"
"Lake-Town, isn't it?"
"Yeah. What happens then?"
"Um..."
"We have to introduce Bard, so what if the Dwarves sneak in on his barge?"
"Yes, and they can get caught stealing weapons from the town armoury."
"That would be very dramatic. Now, isn't there a leader or someone in Lake Town?"

You get the idea. One thing that has always struck me about Jackson's films as adaptations is their inconsistent approach. On one level, they follows the narratives closely, more or less including all the main "stages" of the story on a level of surface memory of the individual episodes "Trolls - Rivendell - Goblin Town - Wolves - Beorn - Mirkwood" etc. Yet the individual details of those episodes often bear little to no relation whatsoever to the text.

It leaves me thinking of these films as "adaptation by hazy memory", like a script written by someone who had an above-average knowledge of the narrative, but hadn't read it in a long time, so they remembered only the broad strokes and not the details; as if, had they remembered or considered what Professor Tolkien wrote closely, that there was no need to fill in the details with their own inventions, as he had done so already, but they had forgotten.

Has this occurred to anyone else? In hindsight I think it's one of the things I find most unsatisfying about the films, and inadequate about protestations of their "faithfulness" - do they retain superficial elements because these signify the narrative in the popular consciousness, but ignore the specifics because they have forgotten they exist?

Are there any other comparable moments from either trilogy? I think "The Lord of the Rings" might be less guilty of this than "The Hobbit", featuring compression over invention, but parts like the Trolls, like Mirkwood and like the last stage of the journey to the Mountain seem to feature this "vague adaptation" quality quite substantially.