Why is disneys the hunchback of notre dame and esmeralder such an underestimated princess?

I agree with you. She's one of my favorite Disney girls. Here are the possible reasons.
1. HoND didn't do as well in the box office, as say, Mulan or Pocahontas.
2. It is a very dark movie, and not really geared to the same audience as the other movies in the princess lineup. For example, you wouldn't want to show your 4-year-old, who loves Cinderella, Hunchback of Notre Dame.
3. In the movie, it is stated many times Esmerelda is a gypsy. Some people see this term as offensive to the Roma people of Europe.
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My guess is Number 1, since you really don't see much merchandise from this movie.

Not a princess, plus there was some kind of scandal when that movies was new with scenes that had to be edited because they were to revealing or something.
Anyway, I think if there's an underrated Disney princess it's Eilonwy from The Black Cauldron.

1. she's not a princess. almost all of the disney "princesses" are born a princess or princess by marriage. mulan is a stretch, but she's from an old an honored family and she's marrying a very famous general and she saved the royal family. esmerelda isn't any of those things.

2. the idea of turning the hunchback of notre dame, one of the darkest and most disturbing adult novels ever written, into a kids movie was such a mind-numbingly stupid idea that I would think that disney wants to completely forget the entire thing every happened.

I don't know but it is a good question