The reason: the ATS-V coupe.
There's been an overwhelmingly positive response so far to the totally kick ass 2016 Cadillac CTS-V. It looks terrific from every angle and, in many peoples' opinions, makes the BMW M5 look somewhat boring. To each their own. There's also been plenty of talk about a potential successor to the previous generation CTS-V coupe. In fact, it's already been rendered by X-Tomi Design. Yes, it's nothing more than the sedan minus its rear doors. It doesn't look bad, but the aggressive look of the old CTS-V coupe isn't there.
But none of this matters because a new CTS-V coupe isn't going to happen. Why would it? Think about it. The reason is because of the also new ATS-V coupe. Having two high-performance coupes somewhat similar in size makes no business sense. They'd effectively be competing against each other for buyers. Simply put, the ATS-V coupe is the new CTS-V coupe.