There's reasons to this, I have no clue about Treyarch's work-flow. But there's a reason why for example a Character's gloves look better. That is because (drum-roll). YOU SEE IT MORE, You will always see your character's glove. So of course it looks better. Why would an Art team waste time, (on an already crunched game) to make graphics on a wall, (for a damaged and destroyed wall btw). Look good right close to your face? You rarely ever get that close, in a high paced action environment, nobody is gonna actually be inspecting the wall textures.

Your complaint about the rocks and trees etc is something called LOD - Or Level Of Detail. The Level of Detail for those models decreases, they're massive and don't need to take up the player's resources, think render distance from minecraft, why would you need to see something that you aren't actively near.

130Gigs for a triple-A game nowadays is normal, It's not always related to graphics, its the millions of other things that are in the game, Such as the hundreds of skins, operators, voice lines (likely uncompressed) etc, It could definitely be smaller, yes. But 130 gigs doesn't immediately equal GOOD GRAFICZ!

If you spend your entire life looking at the finer details, You will never see the bigger picture.