Reason for preventing the two lovers from leaving for Bristol

Hawthorne didn't leave open endings. His conclusion of the novel doesn't leave us anxiously anticipating the next chapter because it isn't meant to. Having the two leave together with Pearl would have been completely unrealistic and would have involved many additional conflicts within the Puritan community. Thus, it ended with declarations of love, the hug from Pearl (previously denied), and freedom for each of them. Different freedoms, but freedoms none the less.