I think he's afraid, and rightly so, of it getting adopted without being understood but then getting more popular than the original idea and drowning it out. It's the same reason people speak against introducing Douglas Engelbart as the "inventor of the mouse" when he was so much more than that. Look at Scratch. I think it's a pretty objectively a bad way to introduce programming systems to children, especially over something like Logo, but it is incredibly popular. And I'm not referring to the so-called visual aspect of it. I think it's just fundamentally a very uninteresting permutation and medium of teaching.