Poetic Justice means that prosperity and adversity are rewarded in proportion to the merits and demerits of the characters.
In Shakespearean tragedies there is no poetic justice but partial justice... for the tragic heroes suffer more than is merited or deserved by their faults; Lear and Othello suffer terribly out of all proportion to their trajic flaws. Moreover, along with the hero some perfectly flawless and innocent people also die. Cordelia dies with Lear and Ophelia with Hamlet.
Poetic Justice is not fact of life and so Shakespeare, the realist, does not introduce it in his tragedies.