The market cap of Ripple (and many of the premined coin/token supplies) is very misleading as often %70 or more of the total supply is in the hands of the founders or an anonymous presale/ICO "purchaser"
i.e. Ripple co-founder owns ~9,000,000,000 Ripple units, and is selling them off en mass:
https://www.coindesk.com/ripple-jed-mccaleb-settle-suit-over...