My guess is that most studios have cut DTS soundtracks out to save money - kind of like when they stopped giving you the piece of paper in the case that gave you the chapter titles. Or how many discs just have the movie title in that generic, colorless font now instead of a colorful, unique label.
Since so few of us care about sound quality, it isn't a surprise. Just be glad you still get Dolby Digital

.
However, a title I saw recently with DTS was Live Free or Die Hard.