Both character’s motivation comes from their desire to protect their family and home.
Moana wants to explore the ocean, and she goes on her journey because she understands that, as future chief, her family and home need to be safe in the uncertain future.
Mulan wants to know who she is, but goes on her journey after becoming the opposite of the only thing she is certain of, (being a woman), so that she can save her family and her home.
Both of them denounce what they ultimately want in order for the safety of their home/family, yet both are rewarded with what they wanted in the first place during their journey because of their growth and selflessness. Moana leads her people to be explorers again, and Mulan finds peace within herself and with her family.
I like them because this character arc shows more maturity than Belle’s from Beauty and the Beast or Ariel’s from The Little Mermaid. Belle and Ariel want more because...they want more. It’s true that both Moana and Ariel want to explore an unknown world, but Moana ends up doing it out of love for, rather than in defiance of, her people and her parents. And even though Belle sacrifices to save her father, ultimately just wants “more than this provincial life”. She doesn’t want to change or better the world. She simply ends up “getting more”. First she had a cottage and a not-so-great guy chasing after her, and now she has a castle and a prince who has changed his ways.
I like Beauty and the Beast, and I’m not saying that Belle is a terrible character, because she does show strength, but Moana and Mulan actively change their environment. Their motivation is centered around something deeper than wanting more: they want to save their entire world. And because they were willing to go to such lengths to save it, they were rewarded with what they desired in the first place.
If fact, they weren’t just rewarded. What they wanted was was always there, but their journey only exposed it. Belle and Ariel went out and got things, whereas Moana and Mulan went out and grew.