As a fiction author who spends hours worrying about individual sentences and whether they're carrying their weight in the overall story--is it advancing the narrative, or deepening characterization, or delivering important information, or furthering my thematic goals, or (ideally) doing more than one of these things at once?--I'm pretty resistant to your claim that books are "often teeming with filler content." Possibly too resistant; perhaps your attempted reading is biased such that this is actually true. Maybe you're trying to make it through lots of things that were originally published as serials, or lack good editing, or have some other reason for the author to have emphasized sheer length over the qualities we usually find motivating. Maybe this is an accurate representation of your experiences.

But I'd like you to consider the possibility that, rather than huge swaths of those books you disparage being pointless, they are instead doing things that you have not cultivated an awareness for. It may be that, rather than being "filled with so so many words that were just exercise in language use for the author and carry barely any information," they are instead filled with passages offering information that you are not currently sensitive to, like music played on a frequency you can't hear.

Fully engaging with art requires an active interest. Art is generally made by people who are deeply interested in their form, and made in ways that reward said interest being matched. The less commercial the art form, the more this is true. Even within specific art forms, there are distinct traditions and modes. Its unreasonable to expect that you will appreciate everything about a particular work of art without developing literacy in those things.

For example, if I say that I find fighting video games boring, that's a perfectly defensible position. But if I say that fighting video games are boring because the developers don't in enough effort to make something other than a thin story about who wins a tournament, then I'm simply wrong. That's a failure to engage with the art on its own terms. Fighting video games aren't about narrative, they're about zoning and rushdown and combos and various other game mechanics. The developers put in lots of effort, but their focus was on gameplay, not narrative. Expecting the focus to be narrative would be an error on my part.

If I made that error, I might also say something like, "Why do these fighting games have so many characters? The tournament story barely changes no matter who you play as. All these extra characters are useless filler." In saying that, I would reveal myself to be insensitive to the vastly different move sets and mechanical plusses/minuses that are the desiderata for the large casts of most fighting games.

(As it happens, I do think fighting games are boring. But that doesn't mean the games are flawed, just that not all art forms are enjoyed equally by all people.)

(And while the large casts of fighting games aren't filler, there are, of course, video games with filler. Triple-A video games often have filler, to be able to boast about, say, 100+ hours of content. Anime series based on ongoing manga often have filler, to maintain their viewership without running out of material. When things have filler, the reason is usually commercial. When The Hobbit was adapted for the screen, it wasn't split into three movies for artistic reasons. Filler is all about money. Most fiction authors are not lucky enough to have any reason to produce filler.)

A quotation attributed to Lord Dunsany: "I see now that keen interest can illuminate anything, and that anything, moreover, has something worth illuminating in it, and that without that interest gates carved by Benvenuto Cellini from two diamonds would merely look chilly."

Things grow in our estimation with the attention we invest in them. Your "rising standard on what feels interesting" could, instead, be a diminished capacity or willingness to invest a keen attention in things that don't immediately capture your interest. When all the things you struggle to focus on are also things that seem, to you, to be fully without merit, then how could you distinguish between those two states?

Perhaps those books you tried are filled with thing that, even when engaged with actively, would still not be to your taste. But when you say they carry barely any information, it's hard for me not to think of "The Machine Stops" by E. M. Forster:

The air-ship was crossing another range of mountains, but she could see little, owing to clouds. Masses of black rock hovered below her, and merged indistinctly into grey. Their shapes were fantastic; one of them resembled a prostrate man.

“No ideas here,” murmured Vashti, and hid the Caucasus behind a metal blind. In the evening she looked again. They were crossing a golden sea, in which lay many small islands and one peninsula. She repeated, “No ideas here,” and hid Greece behind a metal blind.