This comment is probably tongue in cheek, but I think the slowness of Python 3 uptake was mostly caused by a perceived lack of beneficial features to the large

This comment is probably tongue in cheek, but I think the slowness of Python 3 uptake was mostly caused by a perceived lack of beneficial features to the large HPC/scientific computing crowd. Breaking syntax changes (outside some very obscure things like trigraphs) is what C++ has been looking to avoid (for good/bad).