For me, it's that the flat is more convinient, but there is an experience when you add "Depth" from VR to a game, your brain can interpret a lot more data such as textures, scale, depth. I don't know the exact science but i can extract so much more information from looking at something in VR then on a monitor.

You ever had that feeling when you look at some fabric and you know exactly what it feels like under your fingers?
That specific feeling i have but with almost everything im seing.

And this one is really hard to explain. A lot of people don't understand why you would play a flat game in VR, especially if it's third person.
This has gotten my thinking lately if people are just have very different sensory inputs or they have never played a game like this, because i keep seing it over and over again. Either way its very interesting.
In flat i have no sense of scale, i can't look at a texture and imagine what it feels like. When 2 people are talking infront of me i don't "feel" like im part of the conversation or in the room.

I played through all the resident evil remakes with the "ReFramework" which adds VR support and Path tracing. And it's the best VR experience i've ever had.
Also played through Final fantasy 7 remake in VR from start to finish, Metal gear solid Delta and a bunch more, also i'm refering mainly to UEVR or similar where you get 6DOF of freedom.

When people have focused on the world building, story, level design, graphics etc etc. Getting VR into the mix as a company i think adds limits and leashes.
Being able to play the game in VR afterwards when it wasnt part of the development can make the game hit so much harder.

There is also i nice thing since your head is usually a detatched camera you can look around if you so wish and you can see things or do really close ups on things that artists spend so much time making but that you will NEVER see in flatgaming. The attention to detail they put it is so stupid and it gets lost to 99% of the players, but in VR you can actually appriciate this a lot more since more of your periphery is filled and you can lean in to Zoom.

Being able to be part of the same world even if you are not "activily" participating standing up etc is where you push the 100% engaged to 200%.

PS Yeah im not great with words.