Titanic wasn't just a romance movie, it was a disaster movie, too.
Barbie worked because Barbie was hot, and the whole basis of that franchise is, and has ALWAYS been, girl power. Nothing new, nothing destroyed to push a new message or narrative.
Speaking of which, there's a study that Lego did when they were trying to figure out how to get girls into their market. They discovered that chicks prefer Barbie because they get to take established "roles" ( Man and Woman ) with established scenarios ( Life At Home, etc. ) and then play God with the characters. Want Ken to carry in the groceries? Just make him do it. Want Ken to fall madly in love with Barbie? Then that's what happens. Parents are fighting? Act it out with Barbie and Ken. etc.
Whereas boys didn't want to control a character, they wanted to BE the character. They wanted to build the world in their (mostly heroic) image. It was an interesting fucking study. Hell, I've probably mentioned it before.