SketchUp relies on the OpenGL support of the graphics card driver, therefore macOS is regularly not affected by issues related to intel HDs because drivers for macOS are made by Apple themself (surely based on something the maker of the GPU is delivering) and not by the GPU makers as on WIndows.
Because intel HDs have shown in the past, that the OpenGL support depends on the used driver version which additionally might change with every future driver relase, at least recommending them is not recommended.
This does not mean that they do not work but do not claim if not.
Additionaly, the 3D throughput is simply slow because the integrated GPUs were never meant for nor dedicated to 3D modeling: