I believe AC Odyssey doesn't have repeated or so called radiant quests - that's why you won't be playing it for thousands of hours.
Although just to be clear I tend to really dislike repeatable or radiant quests. In FO4 I avoid them like the plague.
My many hours in Skyrim are a mix of playing 3 main characters, one of which lasted for 5 years, and writing a total of 4.5 books on him (Grim).
Besides the deep immersion and role playing I love about the game, which lets me sink so much into the game, it was also my first ever modded game and the first game I learned about ENB and other post processing tools like SweetFX.
Then it opened up screen archery, making mods, making ENB presets, and linking up to the whole modding community on Nexus and sharing stories and images on the image share.
In many ways Skyrim was like the best of both worlds - it was a SRPG I could do myself yet I also had this great community and social online connection outside of the game.
Many of those 4K hours (actually its around 3670 I think - not at home to look it up) were spent making ENB presets which require hundreds of hours of tweaking. Plus I spent many hours testing mods I both made myself or used. Also some of the stories I wrote could take up to 30-40 hours to create the screenshots in-game just for one long chapter.
All that time adds up. But I can assure you very little of that time was spent doing radiant AI or repeatable quests.
Same for FO4 which I am now at about 2500 hours played. Started my 7th play though a few weeks ago and still enjoying it. I don't do as much ENB preset work or story writing, as I really enjoy the game play in FO4 and unlike most other games I play, I love the combat and really enjoy it. I play on survival mode and use mods to make the game harder and immersive ... and just really enjoy getting into it.
That being said its nice to take breaks and enjoy other games so looking forward to ACO and a few other games coming out over the next two years.