Probably because no one is willing to testify against them
Only their customers can detail the bad things they may have done, but they're all too afraid of retaliation to do so. Apple had cooperated with the FTC while they were fighting Qualcomm in court, but eventually they were forced to knuckle under and even a company Apple's size can't risk Qualcomm retaliating.
At least not until they have their own modem enabled across their entire product line, and they'd still have to worry about patent level retaliation even then.