Engineering is all about 'how' and they use models from science, or pretty much any source, if such models be 'tuned' or 'calibrated' to work with getting the 'how' done. Engineering is about specifying things that work and testing and quantifying how well they work.

For many scientists, science is about the 'why', if we presume that they believe there's an ultimate truth to find. Really, they're building concise, experimentally-supported and widely applicable models from the point of view of engineers. Such 'theories' can be immensely 'useful'. Those can also provide suggestions for the deeper 'why' questions.

Philosophy is also about the 'why' but a broader, deeper and more encompassing 'why'. Science started as 'natural philosophy' which means science was a subset of philosophy.

Art is neither about the 'how' or 'why'. The closest one can say about art is that it is about being. Expressing being but perhaps more. Art is transcendence.