[shermanmccoy]

>they're selling them on USDT-USD markets.

My hypothesis is they get dripfed onto these markets so as not to spook them. Or just transferred off to collateralize other trades - hey it's free money to them, why not set up another trade elsewhere while they are in?

It is not safe to assume anything based off market price action. You seem to be assuming there is some essential relationship between volume traded and price. These are market prices, they can be totally irrational, especially if there is some fake news (Tether is fully backed) behind them.