Part of that was the Tolkien nerds putting so much effort into the details, like hand-forging the chain mail and so forth. The LotR trilogy was a labor of love (re: the stuff that was cut to which you refer above), whereas I think this was an obligation, imposed from the top down (especially the bit about stretching the book into a trilogy). And that also is a result of Jackson not having as good an imagination as we might think. LotR, augmented by the Silmarilon and other background materials, meant all the world-building done for the filmmakers. Also the writing style was kind of sparse, for lack of a better word, in describing the action and so forth, which gave them some flexibility with how they showed it. And for decades, Tolkien fans have been playing in this world, so that they had lots of material available to run with.

With the Hobbit, on the other hand, we have a tighter story, that's more intimate with the main character, while all but ignoring everyone else. From the books, the totality of other character's (besides Bilbo & Gandalf) traits are:
Balin - nice
Thorin - brave, arrogant, stubborn, determined
Bombur - fat
Fili & Kili - good eyesight
Bard - cool, badass
Beorn - gruff, hearty
Elrond - wise, helpful

What do you do with that? Meanwhile, there is this crowd of 13 dwarves, whose presence is mostly played for comic effect, while the individuals are glossed over, and the awkward logistics are more easily downplayed on the page, but just saying, "all the dwarves did this" "the rest of the dwarves followed after". So they tried to get creative, at which they were not so good. Part of that is because "The Hobbit", unlike "Lord of the Rings", was not about the world-building, so the same sort of people who were working up the details of Rohirrim culture, or dissecting the differences between orcs and uruk-hai, weren't really bothering with doing the same sort of thing for "The Hobbit". That creative bankruptcy manifested in three separate sequences in "aUJ" with the characters perched atop a precarious, teetering height, swaying to bring them close to one another, and then yanking them far apart (the cliffs during the giants' fight, the scaffolds of the goblin town, and the fir trees at the end).

I remember making jokes about George Lucas' acrophobia manifesting in having characters dangling from heights in every Star Wars film, but he didn't abuse it to the degree Jackson wore out the "high swaying peril" scenario.

That sounds about right, but that could also be confirmation bias. Maybe someone proposed that as a possible title, and the natural counterpart to the title of the first movie, but BotFA is such a more obvious choice, I can't imagine T&BA would have ever been more than a working title, like "Blue Harvest".