JPEG decoding is frequently included in systems with DSP blocks because it’s easy to add to a system that is already doing similar math for video decoding.

It’s not always used when available. It can be a lot easier and safer while being fast enough to do it on the CPU. If the operating system has an image decoder path that will handle everything for you then it might be used (Apple hardware for example) but if you have to go out of your way to implement the API, common software will favor software decoding because nobody wants to maintain code testing branches for different hardware image decode platforms.