Why did shakespeare’s noble character speak in iambic pentameter while commoners spoke mainly in blank verse or prose

To create a distinction between the educated nobility and the coarse lower classes.

Explanation:

Back in the time of Shakespeare, the nobles were generally seen and portrayed as wise people who had access to a superior quality education. Thus, writing their dialogues in such a noticeable metric like iambic pentameter differentiated them from the lower class less educated characters in plays.

that was the type of government the spanish colonists were used to.