It's not a mystery. 36% of mobile devices running Android don't support OpenGL ES 3.0.
Similarly, the desktop and laptop GPU market has been dominated by integrated GPUs for the last decade, and a large chunk of them have issues that require blacklisting WebGL 2 support.
In both cases support is slowly increasing at a rate between 1-3%/month (a little less on windows, a bit more on android). At these rates it can be expected for WebGL2 to reach WebGL1 levels of support (98%):
- Windows: June 2019 to September 2020
- Android: February 2019 to August 2019That would actually be phenomenally soon. Since the issue is GPU hardware, and the prevalence of each generation follows an S-curve, we're going to have a long tail before ~98% of support is reached.
That said, SwiftShader has recently reached the milestone of passing the dEQP test suite for OpenGL ES 3.0, running entirely on the CPU, and we're making quick progress on WebGL 2 conformance. So for the needs of casual games and educational content we could have broad support much sooner.