What is the purpose of grounding rectifiers?
Perhaps you are not understanding that the transformer isolates the secondary winding and the connected circuit from the primary power source. The primary power source may be grounded, but there is no other connection between the primary and secondary. All of the secondary current must flow through the secondary winding even though a point on the secondary circuit is grounded.

A short circuit only exists if two points in the circuit are connected through an unintended path. The only path for current is from one end to the secondary winding through one diode or the other then through the load and through the diode on the other side of the load that matches the polarity of the first diode to the other end of the secondary winding. There is no path through the ground connection back to the other end of the secondary winding or to any other point in the circuit.