I think Tether's goal is to keep the USDT on par with the value of 1 USD. If the demand rises for Tether (because a lot of cryptocoins are dropping in value, a situation we saw a couple of days ago), they need to take action to make sure the demand doesn't drive the price of Tether up.
I think that's why you see these actions.
All of the above is probably also true for SBD by the way, but I'm not the expert, this is just my opinion...