Cadillac, as I see it, right now, has four significant problems.....all of which are affecting sales.
First, many of their most loyal and traditional customers (essentially the WWII generation and some early Baby-Boomers) are dying off, and the ones that are still driving are alienated by the loss of the DeVille/DTS. (this is similar to what happened at Lincoln with the loss of the Town Car). To date, though the CT-6 and Continental Concept both look promising, neither Cadillac nor Lincoln has really developed a credible replacement for the DTS or Town Car...the XTS and MKS just aren't comfortable enough for the seniors and traditional buyers.
Second, the compact-luxury SUV (CUV) market is currently exploding in popularity, and, while Lexus, BMW, Lincoln, Land Rover, and Audi have all recently addressed this with new products, Cadillac is clearly late to the party, and will not have a small SUV ready for perhaps another year and a half to two years.
Third, while there is indeed a market for sports sedans (and the CTS -V and ATS-V are both excellent products in that category), the standard, run-of-the-mill ATS was probably designed with underpinnings and tires that were too stiff for those seeking a nice entry-level Cadillac with some comfort to it....and a step-up to even the non-V-CTS costs quite a bit more.
Fourth, Cadillac's CUE system, like Ford's MYTOUCH, has been a source of complaints, not only just from customers but reviewers and the auto press as well. Sometimes newer and more complex is not always better.
So, it looks like the division has its work cut out for it.