In the play Richard III why do you think Edward blames those who did not ask for mercy on Clarences behalf?
It is Richard who blames the others, not Edward. Edward IV is Richard's brother who is king at the beginning of the play. He's very ill, and Richard plans to become king by getting rid of Clarence, Richard's other brother. In the opening lines of the play, the audience learns that Richard has begun an evil plot to cause King Edward to arrest Clarence by pouring "drunken prophecies, libels, and dreams" into the King's ear. In other words, Richard has started rumors about Clarence that will make Edward suspicious of Clarence.
As Clarence enters, being led by guards to the Tower of London, Clarence pretends to be sympathetic to Clarence and blames Queen Elizabeth, King Edward's wife, for influencing the king to arrest him. He even suggests the king's mistress, Lady Shore, might have done this as well. Richard promises Clarence he will work for Clarence's freedom. After Clarence leaves, Richard is very pleased with how well his plan is going and says he'll make sure Clarence is executed before he can be proven innocent.