Melville was already an established author after Typee and Omoo - Moby Dick was sort of like a Sgt Pepper situation. People expected a sea story and they got so

Melville was already an established author after Typee and Omoo - Moby Dick was sort of like a Sgt Pepper situation. People expected a sea story and they got something quite a bit different. Or imagine if Tom Clancy wrote ten Jack Ryan books and then Gravity's Rainbow or something. Sadly many authors don't get the recognition they deserve for generations afterwards... but the important thing is they didn't let that possibility dissuade them from writing!