The short version: the costs of developing new applications grew too great to justify.
Gone and already largely forgotten, the Cadillac CT6 was a highly imperfect product. Meant as a top-of-the-line flagship sedan that would communicate Cadillac's more aspirational future direction, the CT6 had the right platform for the job - the advanced, lightweight GM Omega platform - but suffered from many of the same cost-saving measures as the rest of its contemporaries, with basic powertrain offerings and cheap-feeling GM parts bin switch gear that belied its no-expense-spared underpinnings.
In 2018, the Cadillac CT6 finally gained the right engine for the job, too: the twin-turbocharged, 4.2L DOHC "Blackwing" V8. Among the more advanced engines in GM history, and with a $16-million development price tag, the Blackwing is, nonetheless, being put out to pasture with the rest of the CT6 model line. But why?
According to Road & Track, you can pin the Blackwing's sudden and untimely demise on shifting market demands killing the business case for more Omega platform models. It won't surprise you to learn that CT6 was not intended to be GM's only Omega-based passenger vehicle, nor Cadillac's only application of the Blackwing V8; at least one crossover was in the pipeline, along with a production version of Cadillac's stunning 2016 Escala concept.
But, the Escala project was binned as sedan sales shrank not just in the luxury segment, but across the entire market, and the Omega-based crossover thus had one less model line to help it amortize the cost.
"At some point, financially, it just wasn't a good strategy," a source told Road & Track. "[S]o one by one, those Omega derivatives disappeared, and in the end, the CT6 was left all by itself."
But there were other forces at play, as well. GM was in the midst of dramatically overhauling its high-margin, money-making body-on-frame SUVs, leaving fewer engineering resources available for new applications of Omega, and ultimately, Omega and Blackwing were part of former chief Johan de Nysschen's long-view approach to Cadillac reestablishing its aspirational bona fides. GM tends to be averse to such long-view strategies where there's no immediate path to profit.
All of these forces conspired to keep GM's brilliant Omega platform and its sophisticated Cadillac Blackwing V8 limited to the slow-selling CT6 sedan, the automaker deciding to cut its losses and walk away. It's a darn shame.