I totally do that too, always, in every game. I had like 60 open pending quests in Skyrim through half the game and when I ended up actually doing a quest I often had no idea who gave it to me or the story context about it. It'd be nice if there was a way the game could limit the number of active open quests without stopping you from doing things. I'm not sure how they'd go about doing such a thing in a way that isn't immersion breaking but there has to be a way at least for some potential quests.

I just started playing that when I finished The Witcher 3 last week. I made it to where you fight "the beast" in the Outskirts and it kills the witch before I can kill it and the ghost dogs it spawns, then it kills me. I've tried just about everything to power up as much as possible and find it impossible to proceed. ;o/

I watched some videos of people doing that fight successfully but it looks mega repetitive running away all the time then going and hiding on the porch of a house, then running around again, reminds me of button-masher platformers or games like megaman from the console days fighting a boss monster and you had to wait until it opened it's mouth and time your shot perfectly or similar. Annoying.

I ended up reloading from an earlier save game so that I could skip that fight and go do other stuff hoping I could level up some more and go back and try to fight it again without the witch dying. There aren't too many open quests, maybe 10 or so but some of those are just quest+subquest type stuff. Overall I'm enjoying the game, but finding it really needs a horse, or to remove all of the god damn fences in the Outskirts. It's "fetch this from the other side of the map" then running around a twisty maze of fences you can't jump over or ride a horse to get to the destination fast, then return the same way, then another fetch this, several more times. I took a couple days break from it for now to do something else.

I usually start to lose interest after 7 months of gameplay.

I don't agree with the "too long" characterization at least for myself anyway, but I agree with everything else you said and I too want to "do everything" if presented an option. If something turns out to be boring, I don't consider that part of the game "too long" though, I just consider it "boring and I wish they'd change that to something else". I want the game to have that extra time to play it and if given the choice to have the developers do what I want, I would choose "replace this boring part with something more fun" rather than "the game is too long remove this boring part and make the game shorter" any day, although there are some cases were removing content wouldn't be a bad idea too.

A good example of this is The Witcher 3 - I love the game and want it to be 3000 hours long if possible, but it isn't. At the same time all of the "smuggler's cache" quests marked by "?" in the ocean around Skellige are the most boring and useless part of the entire game and there are about 30 or 40 of them or it sure seems that way. Next time I play through the game I'll dread having to do all of those again because it was so mechanical to go in the boat from one location to the next with the exact same enemies each time doing the exact same attacks to get the exact same (useless) treasures. I think they could have made those ocean based "interesting areas" actually interesting. Maybe throw a hydra in there to fight, or that whale or something, put better treasure. Or put less directly in the water and more locations on the various small islands to explore. I'd have much rather had that than the tonne of duplicated "?" locations with crap loot personally, but it only took a couple hours to go to them all so it was a relatively small part of the game overall, and I broke it up into 4 or 5 "missions" so I didn't have to do them all in one shot.

Well, an informed gamer doesn't even need to read the back of the box. You know what you like and what you want. That is great!

People new to gaming (or RPGs in particular) don't know very well what will be more relevant or meaningful for them. The same is true for parents who are looking for a game to give their kid on their birthday. They need to fall back to something they understand as to make a decision. More stuff = enjoyed longer. Simple!
Maybe today this is no longer true, but in the 90's and early 2000's people made their choices in the store. With new methods of distribution, things seem to be a big different, with DLCs and expansions becoming more common and a shift of mentality in the devs and publishers.

Another factor is publisher interference. "This game needs to last at least 40 hours". Would you care to guess why Arcanum even has a multiplayer mode? You don't play the same game, and you can't save your progress.