Probably an odd question as it pertains to myself specifically, but I thought maybe others here have had similar experiences and can tell me.
When I was a kid I used to really get immersed into the games I played; I'd feel as though I was actually, feeling the very walls around me in dungeon crawlers, getting tense in fights and such, but nowadays I don't really get that sense any more. I'm in my mid-30's and now I'm thankfully able to afford any game I wish, I thankfully can choose how long I spend gaming, yet I just can't get immersed, I just can't get pulled in anymore.
My buddy told me about the Witcher 3 and told me it's great and immersive like only the oldest games ever were, and yet when I played it....I got kind of bored, and lost interest somewhat fast. One possibility is that maybe with modern proliferation of game knowledge, we can simply google for anything we want rather than let the game help us find what we need, pulling us out for that much of the game, another possibility is that we recognize mechanics and animations for what they are, and we try and memorize enemy combat animations, and our own iframes and such, even if instinctively.
I honestly can't remember the last game I played where I got immersed into the game and just felt the world rather than just see it.
I like the description of Outer Wilds as a space archaeology simulator. Calling the solar system "small" isn't wrong but I think it's better to call it "efficient." It's incredibly dense with stuff to find, no padded travel times, any empty space is visibly empty and mostly just exists because planets need a complete surface, you can just go to explore the latest hint you found and be there in like a minute, tops.
Subnautica is less densely populated, has more empty space and waiting, but I do think there's something to be said for the sense of scale that that adds. Outer Wilds makes the world feel big by making it super intricate and constantly moving, Subnautica is more literally big, less alien, and can be kind of meditative because of that.
Aldo they're both "long-take" games like Dad of Boy, with no loading screens or cutscenes except at the very beginning and end iirc.