Why are most of the Disney Princess movies musicals?

A winning format requires a good script, making it more complicated would be adding songs and lyrics - for a while Disney had the best writing team available and won oscar after oscar for best original song. My theory to this question is that songs are added to the movies because the stories are pretty boring (for children) without the songs, and in some cases pretty short. I mean how long is beauty and the beast if you don't have the musical interludes (sorry, still the best disney movie ever)

I think also it is a factor of time/place - in the 80s/90s they made a lot more musicals because they WERE successful - they don't make as many now (I'd wager Disney releases much more 'non musical animated films' just from disney, not pixar, than musical ones these days), just like hand drawn animation (sadly) is a dying art, musicals come and go. Animated films also take a while to make so the impact of a film like frozen could take years to be felt on screen

It's mostly just the Disney style. Disney makes more animated movies than just the princess ones. A few examples:

• Pinnochio has songs and no princesses.
• The Jungle Book has songs and no princesses (except for that human girl at the end who doesn't speak/sing on screen).
• Peter Pan has songs, but Tinkerbell (not a princess), Nana (a dog,) and Tiger Lily (sort of a princess) never speak or sing. Wendy (not an actual princess) is the only female-presenting character who sings, although her mother does speak.
• Jasmine, who's an actual princess, doesn't have any songs of her own in Alladin--just a duet with Aladdin.

It's mostly for marketing. Children (and people of all ages) like music. Also, music often helps people memorize things. Memorable songs help to make the films more appealing, and thus, more financially successful. The same for the merchandise.

Many of these movies have children as a main target audience. Children like to sing or hear singing when they are being entertained. Sesame Street used that to great effect. And I am sure there are other children's programs that choose that format to keep children's attention.