That is not due to a writer's preference, it is how Larian approached the EA feedback regarding characters in general.

Shadowheart's entire character was adjusted as fanservice in EA, her first version was not so nice towards the player. Her old character is still visible in her interactions with Lae'zel, since that remained unchanged. Funny enough they have mellowed her towards a githyanki protagonist, so now she just hates Lae specifically. As a result her character (like some other companions) is now a bit of a patchwork, includign her romance. Which I'd describe as playersexual, because while Shadowheart has her own preferences, she doesn't really state them unless in reaction to whatever the player does.

Larian have done the same with Halsin (most players wanted him in the party because they wanted a good aligned companion, but Larian instead went with the sex meme), and Wyll (they rewrote his story so that Mizora is basically there to offer sex to the protagonist, and you cannot throw her out of the camp).