Moonbyul was kind of forced into rapping by her company. She has said that she's grateful now for her position and how she's seen as a rapper, but she didn't want to rap at first. She wants to be seen as a capable singer who can also rap.
I can't remember the more recent interview I saw about her current solo work, but in it she said "I'm a rapper only within Mamamoo", which I don't think means she never raps in her solos, but that she's more focused on her vocals outside of the group.