Why did he start a research direction that 50 years later "might turn out" to not be a good idea?
That's a relatively silly question, don't you think?
Sounds like sour grapes. He worked on it for a long time but he doesn't own a trillion dollar company. Missed the boat?
No it's a completely serious question. The goal has always been to replicate human/biological thinking processes in software, and now that this has been more or less achieved he's suddenly not happy about it. There's been plenty of opportunity to actually think about "what if all of this actually works" but they chose not to.