Spherical Harmonics became extremely trendy in the graphics literature for dynamic lighting and pre-baked light maps of some sort, and completely dropped off at some point. Still remember some discussions and questions regarding how they're not easy to "orient".
They're an excellent solution for dynamic objects w/o too much hardware reqs(PS3 era HW should handle it easily), I think they're still used in tons of places.
It's just that most usage is through finished impls on lower end HW like Unity, Godot,etc and those that implement their own engines these days probably skip them for more global methods directly or just go for good-enough simpler solutions to get "gi-like" appearance like screen space ambient occlusion and/or cubemaps.
Also I think once people finds Greens walkthrough they can get much from it (or give up).
