To act as the Devil's Advocate here, I suppose the very high valuations for the AI companies are because some people think AI will solve those through allowing robots to do that work. Although, Healthcare is a lot broader, and seems to me to be much more complicated than the others. Surely less solvable than the others in your list - if any are in the near future.

Healthcare is probably the one that we need some sort of help with the most! I think the need for people (fine - or robots) working in Healthcare will grow faster compared to the others in the future because of population aging.

Edit: Clarified my meaning by adding "some people think" to the sentence "...because some people think AI will solve..."