Processing might not be directly relevant in industry, but that's about the only thing it doesn't have going for it as a computing playground / way to get started with programming.

* Terrific official documentation (not just API docs but plenty of high quality examples and tutorials that are beginner-friendly without being stupid or patronizing)

* A couple great books (Nature of Code)

* Some great third party tutorials as well: https://funprogramming.org/

* Dead simple to get running; dead simple to start getting nice animations on screen; small and focused API; hot reloading

* Inspiring community filled with intelligent, creative people at the intersection of the arts and academia