The idea that “data has gravity” means it has persistence; a fixed state. Because of this fact, storage management often requires you to move lots of stuff, which makes it heavy. As a result, the process takes a lot of time and a huge amount of bandwidth, both of which are costly.
The process is also a very risky one, for several reasons. You’re fundamentally changing the data every time you move it, so its integrity is at risk. The more people who touch it, the greater the risk of error. Crossing international borders creates legal risks. And underlying it all is a financial risk.