> Probably because it uses TensorFlow (lite) and there aren't many (any?) VPLs supporting C++ integration.
which VPL do not support C++ ? all the major ones have externals / plug-ins / modules that can be written in C++ - Max/MSP, PureData, LabVIEW, vuo, BluePrints, vvvv...
AFAICT the relationship for Scratch is that Google wrote a new VPL (Blockly) and the MIT Media Lab released it as Scratch 3.0.
I guess the "thousands" is from https://opensource.google.com/? In a few minutes of browsing, I couldn't find anything besides Bullet that wasn't just Google releasing something as open source.
I wonder why they didn't build it on top of one of the gazillion flow-based visual programming languages instead?