She's a character, not a person. As such she 'desires' to be whatever the artists and writers decide.
Her last pose could only be described as "Here's my ass". It had no nuance, and it seemed detached from Tracer's characteristics; it wasn't fun, or energetic. This one, by contrast, is better - if you want to see her as having a "desire to be sexy" it doesn't take away from that, but it also isn't her just doing an ass pose.
The change makes sense to me. It isn't about being prudish with the characters, it's about portraying the characters in a way that makes sense instead of giving a character a generic 'be sexy' pose.