From what I've gathered. It's either about nostalgia and/or being more crude looking. Sometimes it's completely arbitrary often boils down to 'new thing bad, old thing good'
I don't think that's either an accurate or an honest summation.
DeepEnigma
an attempt at an honest understanding of what people mean by soul in this context:
People see greatly adored originals as games that were loved in the first place because they were greater than the sum of their parts. Everything crafted for that specific experience. In RE4's case, part of that is what Mikami directed, and it's no coincidence that he's renowned. It's not a coincidence that 4 has been loved for so many years by so many. The soul would encompass the personality, the atmosphere, and the execution of the various things it aims to accomplish and in almost intangible way. I suppose it's the idea of the devs putting their heart and soul into a project and it showing.
By their very nature, remakes are working to make something that already exists, and even when Capcom reimagined RE2-4 the goal was to recreate and modify. By design that deviates from the original, and people see the changes as lesser than as a result. If you try to recreate a puzzle with different pieces it's not going to look the same when you're done.
Some things are likely inevitable, as advances in graphica mean you can't put out the same game with the same comparatively simple visual design, and that road is perhaps what leads to yellow paint on every interactable object in the game. Is it avoidable? Yes, because not every game does it. But the real reason they did that is something we will never know.
Is nostalgia part of it? Sure. Do people romanticise the original and it's development? Probably. Both sides of any internet argument attract equal amounts of "Look how ridiculous the other side is being", and this is no exception.
The fact is that remakes will always be compared to their originals, and there will always be an inherent bias because people love or hate the original.
The word "nostalgia" has turned into a go-to word to dismiss criticism, and that's intellectually dishonest.