I think i would like to argue this often used argument: "if you pay attention to the terrain quality trackside while driving you do something wrong".
Of course you are not focusing on the trackside terrain and vegetation when driving but that does not mean that your view is limited to the area of the actual track/road. You do see more, for example on straights, if i dont play competitive e-sports, every now and then i look around, i look at a tree, i look at the hills in the distance, i look at the sun rays. When you take a hairpin and you are sort of slow, then you maybe even get how the terrain on the other side of the barrier looks like although you focus the apex. And it adds to the immersion alone to know that you are driving in a game where the visual quality of all elements is on a top level. Of course i dont expect the track side bushes to have the same level of detail as a curb, but its also not completely irrelevant either. When the different areas of the game are too much apart from each other quality wise, then it impacts the game's coherence for you and ultimately how you perceive it. I think that PCars2 is a good example for that. Track surface, curb detail and cars look great, but i find that the quality of everything else on their tracks is too far away from that quality and because of that i have always a slight feeling of: the game is not finished. Its not a coherent unit, it feels more like stitching together parts of different quality.
