Why Hasn't the FDA Approved Cohesive Gel Implants for Buttock Enhancement?

I am not an expert in the FDA approval process, but unless a manufacturer spends a lot of money doing the research necessary to get approval, and then submits that research to the FDA, the approval process would not even get started. I am not aware of any manufacturer who has submitted an application to have cohesive gel implants approved for buttock enhancement, so I would not expect any FDA approval to be forthcoming anytime soon.