In Q3 2020 stablecoins were moving about the same in daily trading volume than the country of Japan. There's been speculation that it gained popularity for moving large cross border transactions with a much faster settlement
And this author proposes that if the US and other countries ever make stablecoins illegal they'll move to the next best thing, the new digital RMB from China.
So it's in the best interests of the US to protect the dollar as global reserve currency by letting stablecoins continue