It doesn't say Ripple Trade is not available to US citizens.
It says the gateway called "BTC2Ripple" will no longer be available to US citizens.
This is most likely necessary to be compliant with FINCEN regulations.
And FATCA, KYC sufficiency, and FCPA and Withholding Agents, and a bunch of other regulatory barriers to doing business with US
victimscitizens.