Arbitrary numbers are boring. Nobody reads newspapers to read about numbers. People read newspapers with stories about violence and scandal. I would rather hear about the Bitcoin CEO being the terrorist mastermind behind The Honey Boo Boo show.
I'm pretty sure the number 10,000,000,000 written that way would catch anyone into reading the article.
When you are investing you notice the market cap has gone below or above another billion. The ten billion mark is a big marker, like when the price of an individual bitcoin goes below or above another hundred dollars.