Cause right now it's a soul-crushing grey. I personally like to use https://media.moddb.com/images/mods/1/16/15914/Cybran_ACU.jpg for mine.
Would be cool to have a default background for the client.
We had the one you linked as default and receive a lot of negative feedback, so we move to a neutral color instead 
"Nerds have a really complicated relationship with change: Change is awesome when WE'RE the ones doing it. As soon as change is coming from outside of us it becomes untrustworthy and it threatens what we think of is the familiar."
ā Benno Rice