@Norainhere They basically got shipped not only cause Cassandra is implied to not be straight, but also because at one point in the series Rapunzel herself literally states how much she loves Cassandra. I don't remember very well but I think Rapunzel also called Cassandra her soulmate.
That is common. You also read stories about poets where you never read their poetry. The artist/author doesn't want to take the risk of hyping the art of the protagonist in the story and then presenting their own art and having people feel disappointed in what they saw/read. It's one of those self-preservation things creators do to prevent looking back at their work and cringing. (The way Billy Joel does about the song "C'était Toi (You Were the One)", about which he has given aspiring songwriters the advice to never write a song in a language you don't speak.)