Again, look at Far Cry. People were sick of the formula after a small handful of games. Same for AssCreed and such.
Bethesda could release TES VI tomorrow and it could be on Skyrim's level of quality with all Skyrim's systems, but you know it wouldn't be received as well as Skyrim was 13 years ago. If it was very competently done (which Avowed obviously won't be) then it'd probably meet with reasonable reception and develop a solid fanbase but you can't just keep treading water over and over again and releasing reskins of the same game (on the same shitty engine, in Beth's case) and not have people start to question what the point is.
The problem of Far Cry is that it is indeed a formula. Elder Scrolls, so far, has not been, at least not to the same degree (though Skyrim, ironically the most popular entry, is the most formulaic).
Elder Scrolls games have plenty of hand-designed quests, factions to join, lengthy questlines to go through, etc. Even in Fallout 4, which is filled with markers on the map and which has the weakest quests of any Bethesda game, you can explore areas and talk to NPCs and not know exactly what you're gonna get. Might get a fetch quest, or kill quest, or something more involved with a cool little story. Might enter a dungeon and find some cool mysteries and a unique weapon at the end. While the games follow a similar structure and design philosophy, they are not simply copypasted formula like the Far Cry or Ass Creed games.
In Ubisoft open world games, you know exactly what you're gonna get when you go to a place. Side quests are all forced into a mold: each one corresponds to a certain activity, no exceptions. There are the car race quests, there are the hunt animals quests, there are the kill a specific enemy quests. And unlike an Elder Scrolls game, where you enter town and talk to people and they give you quests and you don't know beforehand how the quest will play out, the Far Cry formula just slaps a bunch of symbols on the map (so you know exactly what kind of side quest you will find when you go there) and you go there and do the quest which plays out EXACTLY like all the other quests with the same symbol.
People aren't getting tired of Far Cry because they're open world games. People are getting tired of Far Cry because there are no surprises and all the content is complete copypasta. I know, because I played them, and even the weakest Bethesda games have more gameplay variety compared to that formula slop.
You don't need to innovate to make a good open world RPG. Just literally copy Morrowind or Skyrim in its mechanics and open world design, and then just design some really good and unique quests, a world that looks unique and has cool shit to discover, and you're golden. There's a reason mods for these old games get such a positive reception, just look at how popular both Tamriel Rebuilt and Beyond Skyrim are. They give you more Morrowind and more Skyrim... with high quality hand-crafted dungeons and questlines that aren't formulaic.
If someone were to make a modern Morrowind or Skyrim, it wouldn't need any unique new mechanics. All it needs is quality content that isn't just the same 5 quests copypasted over and over and over, and it would sell like hotcakes.
As much as I hate Oblivion for what it did to The Elder Scrolls and RPGs in general, its quest design is still praised to this day and I can totally see why. It had cool ideas and stories. There's a quest where you enter a painting! There's an assassintion quest where you enter a holiday house alongside other guests and have to kill them one by one without anyone noticing you're the killer! Sheogorath's daedric quest ends with him making literal cats and dogs rain from the sky! Those quests are fun and interesting because they're unique and memorable. There aren't 10 quests where you enter a painting. There is exactly one. In an Ubisoft game, there would be a dozen and they'd all be marked on your map with a painting symbol. If an Ubisoft game has one good idea, they're not content with using it once, they gotta copypaste it again and again and again until it stops being fun and turns into a chore.
People have even grown to like Cyberpunk 2077 despite its massive flaws, because it has cool quests with unique ideas and good writing. Same with Witcher 3, which has shit gameplay and systems, but great quest design.
People just want to explore a cool world and discover
unique content in it. Get that right, and your game will be a hit. Do the Ubisoft way of copypasting all your best quests dozens of times, and people will grow tired of it. That's all it is about.
