It might be a matter of "do as I say, not as I do". If you look up prior FDA violations, you'll see the FDA get pretty ticked about not clearly laying out the safety risks of a medication - as such, using language such as "our drug is safe" would go directly against that.

The FDA is incredibly strict when it comes to advertising. I remember reading about one violation where the ad had a tagline for an ADHD medication "So you can concentrate on the important things" and showed a picture of a child studying. The FDA said "the image implies that your medication will improve the ability of a child to study and you have submitted no data to the FDA to support this claim".