Some people have scripts that automatically move currency to either: 1. themselves at a different address in a misguided attempt to make their coins more anonymous. 2. to (nearly) continuously pay for something, in a certain case people are actually renting bitcoin mining servers, with bitcoins. Yeah, it's kinda messed up, but it comes down to the unknown forward difficulty rate. The person renting out the server thinks that it will go up in difficulty more than the person that is renting it.