This is exclusively due to MipMapping and texture filtering. The farther from the camera, the blurrier the texture becomes. This is important to prevent aliasing, moiré and shimmering.
You actually have explicit control over this. Here is an example of a grid texture using default computed mips, vs a texture using explicitly derived mips. I’m using DDX & DDY multiplied by some value that satisfies a compromise between blurriness vs shimmering. This is a setting within the texture sample called MipValueMode.
In most cases the default engine calculated mips look great, but sometimes it’s appropriate or even necessary to derive them in some other way.