Traction control can selectively apply the brake to the wheel that it thinks is spinning too fast. If the wheel isn't spinning too fast that that can throw the vehicle into a skid (the reason traction control exists is to avoid going in to a skid).

So it's not just decelerating the vehicle, it's decelerating the wheel that it thinks is rotating too fast to make it match the speed of the road. When in a curve as described by the OP if the wheel is a front & driven wheel this could cause severe understeer causing the car to move further out, which will in turn cause the inboard wheels to slow down further relative to the outboard ones. This could cause a positive feedback loop. Note that if you start braking one wheel that's on a diff the other wheel will attempt to speed up.