Fanboys, you can blame Amy Schumer for this.
Disney has seemingly decided that it's time to put "Slave Leia" merchandise out to pasture. According to rumors reported by MakingStarWars and comments made by artist J. Scott Campbell on Facebook (which he has since expressed regret for), Disney is keen to distance itself from the risqué costume.
Conflicting reports have arisen over the years about the iconic outfit's origins. Carrie Fisher is quoted as having said both that she "had to" wear it, suggesting it wasn't her idea, and at other times stating that the outfit came from her own desire to wear clothes that showed off her female form. Apparently, she felt that the costumes she wore in the first two films were so baggy that you couldn't tell she was a woman.
However it came to be, the costume has popped up in numerous films and television shows, and is frequently worn by scores of young women at comic book conventions. The most recent notorious usage was by Amy Schumer, who was photographed in a replica of the costume for GQ in poses that amped up the sexual innuendos to the point that Disney was compelled to issue a statement saying that the Mouse House never approved of the photo shoot. It's very possible that this is what sparked the notion of retiring merchandise related to the costume.
Over the years, there have been toys, t-shirts and other assorted merchandise made that feature Carrie Fisher in her most famous costume. But of course the most famous merch of all has to be the costumes you can pick up at the store or online. These days, Carrie Fisher is much older and appears to be serving as a leader in the Resistance, in Star Wars: The Force Awakens. So maybe it's best to put the past in the past.
But take heart, Slave Leai fans. This simply means that officially sanctioned and licensed costumes will no longer be made. Knockoffs will no doubt still flourish in abundance.