How the heck does it move so fast?

I have a chair mat at my desk, which doubles for use with the computer.  I'm constantly pulling it out away from the desk, and a few days later, it's right up against the desk leg again

I know the grain of the carpet causes things to move, but how does it move so fast?  And, this mat has 'spikes' on the bottom to keep this from happening.  So how does it happen?  And so fast?  I mean, within 5 days it goes from the picture on the left to the picture on the right.  Does it have something to do with the earth techtonic plates moving and causing earthquakes?  It's got me puzzled.