Can you tell Moll's many suitors and husbands apart? It's kind of tough, right? Sure, some of them are more honest than others (the Banker), some of them are con artists (Lancashire), and some are drips (Robin, the Colchester brother). But for the most part, it's one long string of unsuitable men.
Apart from that, are they really all that different? They're all white men of the same approximate age. They are, for the most part, nameless, and often all we get when it comes to what they look like is a vague physical description. You'd be forgiven for losing track.
One thing they unquestionably all have in common is this: each of them shines a light on one key aspect of Moll's character. Her relationships with each man show us that she is the one in control. Even when the men try to trick her, she's the one who comes out on top. Because of this, we end up with a much stronger sense of who Moll is than who any of her romantic partners are. Then again, she is the one telling the tale.