In the Power Plant Cycle, after all of the energy has been extracted and converted to electricity, the steam must be converted back into water. This is the purpose of the Power Plant cooling systems. This heat is typically dumped into rivers, lakes, or waste heat reservoirs.
Instead of dumping the heat into the environment, this “low temperature heat” can be used to generate electricity at high efficiency via the Lurtz Cycle.
Why hasn’t this been done before? New ideas take time to be understood and implemented.