Why do you think shakespeare used different types of meter for nobles, commoners, and witches

He used different types because he wanted readers to enjoy the full rhythmical poetry of his plays, understanding each character. For this to happen, audiences should know some principals of Shakespeare verses.

Shakespeare possessed great mastery on the use of language an meter, that he was able to disregard the rules and regulations he once observed.  When he wrote most of its plays, he did so in groups of lines so every group produced a different effect, although the metrical was not exact.

Shakespeare used the term "iambic pentameter", in most of his plays, and wrote them in black verse, which means that the plays used meter but no rhythm schemes. An iambic parameter is a common verse in English verse an has a number of ten syllables in the line with an emphasis on those syllables.