This and probabaly lack of company push in this direction (noone is interested and they don’t need dynamic GI for their games).
This topic will be probabaly back at Epic when Fortnite will be under active development again (if ever). Since it’s the only game that requires fully dynamic lighting.
And this too. There is how many people working at rendering exclusively ? 3-4 ?
For engine of this scale is drop in the water. Crytek at their peak had entire R&D section dedicated for real time rendering (and say what you will, but it shows).
There are some new interesting GI techniques like Point Based Global Illumination (which could partially precomputed for static objects).
Distance Based GI is probabaly dead end (simply because it have limited range, which is even lower than Voxels). Although reusnig existing data structe instead of introducing new one incompatibile with rest, is always nice.