I think it's because of the talent behind the songs, and the lyrics. Some 映画 use iconic 音楽 like Tchaikovsky's. He made some of the most 人気 themes in all of classical music. They also have award-winning composers like Arnie Roth. Other times, they use teams of writers who have worked together before and can come together and make great songs (The Rock 'n Royals soundtrack).
There are also beats that make あなた want to sing and dance. あなた could listen to the バービー as Rapunzel 音楽 to relax, and the Princess & the Popstar 音楽 if あなた want to party! If あなた want something funny, listen to The ラット Song from バービー as the Island Princess. 音楽 for Christmas? Listen to the Perfect クリスマス and クリスマス Carol soundtracks. Then there's the lyrics. There are inspiring songs like "I'm On My Way", "Only A Breath Away" and "Making My Way". There's probably a バービー song to suit every mood, and I think that's why they're melodious and touching.