Back in 2004 when the STS was introduced as a 2005 model, Cadillac was the poster boy for America's auto industry (if there was such a thing). Buoyed by its well-received CTS sedan and high-profile -- and profit-rich -- Escalade SUV, the STS was supposed to really put the bricks to the European luxury establishment.
Instead, what we got was a more conservatively styled sedan that has never managed strike fear into BMW, Mercedes-Benz, Audi, or much of anyone - much less deliver awards from the automotive press or (more importantly), solid sales numbers. In fact, owing to its large-for-its-class size, the CTS was an appreciably better car for less money with few penalties, and the second-gen CTS has rendered the STS all but completely redundant.
To be fair, there were slow sellers in Cadillac's portfolio back in 2005, but they were either low-investment niche vehicles (XLR) or at least enthusiasts' darlings (SRX). The STS was neither, and even a high-horsepower STS-V version hasn't been enough save the range from obscurity and flophood.