I'm just as baffled by the whole thing as you are. Our idea that all reality exists simultaneously in time and space may be just as misleading as the appearance of time flowing like a river, from past to future. Perhaps both are just different, but incomplete versions of the real thing. I believe they are both misconceptions born from our need to make sense of things, and the result of us missing something that ties them together. Think: the blind men and the elephant.

I don't know, nobody does. The physicists make these weird assumptions that meet the symmetries of their mathematics and their observations and it helps them make valid predictions about atomic particles and gravity waves and multiple universes. What that all has to do with the universe we actually interact with, the chemical, biological, psychological, cultural, historical universe we actually live in, I don't know. Yeah, yeah, I know they are intimately connected, but until we know how, it is all meaningless to us.

Maybe it has to do with dimensions. Have you ever read Abbott's "Flatland"? The two dimensional creatures of that world are smart, and they are observant, and they are good mathematicians, but since they can't see the third dimension, and since they can only think of it mathematically, they just can't grasp the world around them, even when a helpful 3-d human tries to explain it all to them. The Flatlanders can see the shadows of 3D objects projected into their space, but they cannot see the objects themselves. Look up "Tesseract". Its the 3D shadow of a 4D
hypercube, projected into our 3D space.

https://en.wikipedia.org/wiki/Tesseract

Maybe our inability to see some higher-level dimension makes it impossible for us to grasp the true nature of reality. I've always suspected there is at least one other dimension, perhaps many more, but I haven't any clue as to what they might be.

I'm just speculating, but I think the next dimension is "Complexity". An event in space time can be described as a manifold in (x, y, z, ict, C). We have just started to explore this dimension using fractal geometry.

But I'm just speculating. Maybe our brains simply cannot understand the nature of reality, even if we are capable of partially describing it using abstract mathematics.