With Slave Leia it's out of respect for Carrie Fischer who spoke out publicly about the problems she had with the character's slave costume and how it was later used.
I don't know about Padmé, but I can tell you that on the old forums before we got Padmé the people who were advocating for a bare midriff used a lot of sexist language that, I think, ultimately didn't help their cause. If you want everyone to think that this is a perfectly fine way to portray the character in SWGOH, they probably shouldn't have made degrading/objectifying comments on the SWGOH forums. Ultimately it probably didn't come down to those comments in CG's decision making, but there's no way that went over well.
Personally I'm resolutely opposed to Slave Leia, and while I wasn't automatically opposed to ripped-costume Padmé, I turned against that idea pretty hard reading those old forum posts.