Adobe is also old, as software vendors go. I have no knowledge of their internal workings but it wouldn't surprise me if they still have some code in a product

Adobe is also old, as software vendors go. I have no knowledge of their internal workings but it wouldn't surprise me if they still have some code in a product that predates the existence of C# or Apple's adoption of Objective C. They also have a need for algorithmic speed, and C++ has long been a prime tool for that.