The only one I can think of is someone had drawn leaves in such a way it looked like they just used a brush (they said they drew it all themselves but I could see how the staff may have thought it was a brush) and since the whole CA was the leaves that may be what they are trying to avoid, using *only* premade brushes in ca. which is understandable. On another site I'm on where users can do art things to submit, they want to avoid the use of premade brushes/sticker brushes cause it looks too flat, but I use a brush for like stars and speckles which is fine. I haven't seen any other issues, but I haven't been as active in the CA community the past few days due to irl stuff. So I don't think it's a case of "never ever ever use brushes" it may be a case of "don't make the thing entirely out of brushes" (someone correct me if there are other examples of this, I only know the one issue with stamp brushes)