That's the thing about eye candy. Higher resolutions, better textures, antialiasing, anisotropic filtering and all such graphical innovations are not strictly necessary for gameplay either. Yet the industry keeps pushing them on. I do find that exciting in its own right.
Oh I agree that it is exciting, but most improvements don't really make a difference overall. It's like trying to remember the difference in graphics between a PS2 and a PS3. Sure, the PS3 was better (it was 720p while the PS2 was SD) but beyond that it wasn't a huge difference. The game-changer was tessellation because it made for almost infinitely-small polygons that were all triangles. That made it possible for an object or shape to be properly rounded and incredibly detailed even without anti-aliasing. Tessellation was transformative because it affected shapes and textures of everything. Things like that I find VERY exciting.
But your brain did. You don't have to have a conscious awareness of it for it to improve immersion.
I don't really find that to be true. I say this because from an immersion standpoint, the gameplay and story are far more important. For example, I have NEVER played a game that was more immersive than Silent Hill 2 and that game was released 20 years ago. Compared to today, the graphics were rather crude but the immersion was 100% for the player.
Reaching 100% immersion has also been accomplished by:
Star Wars: Knights of the Old Republic 1 & 2
Skyrim
Far Cry 3, 4 & 5
Assassin's Creed: Odyssey
Crysis
Crysis Warhead
The Wolfenstein Series
The Doom Series
The Witcher 2 & 3
(There are more I'm sure but these are games the I've played)
So far I've only listed locally-played games. Consider the immersion-level in successful online titles like Star Wars: Galaxies, Star Trek Online, World of Warcraft and Second Life. I refuse to try WoW because some people have developed issues separating it from the real world. That makes a game dangerous because it's TOO immersive. However, no online game has incredible graphics because it would limit the number of people who could play and enjoy it.
And then of course, there are the incredibly immersive e-sports games like PUBG, Fortnite, R6S and CS:GO that use the lowest possible graphics settings to maximise frame rates.
Speaking only for myself, I don't believe that eye candy makes me more immersed in a game. Others may be different but I didn't find Skyrim to be more immersive than Silent Hill 2 despite the fact that there was literally ten years between them and the graphics weren't even close to being comparable with each other.
I suppose that, as with anything, YMMV.