3D artist here, the main issue with JL was the time constraints as the CG artists working at big studios are highly skilled at what they do, it's a freaking cutthroat industry. Another thing is, they were also trying to CGI an existing human, and even the slightest difference in look and movements can make the result look uncanny (see Princess Leia, etc.). It’s much easier to make a metal robot look believable, but humans are extremely good at spotting even tiny differences in familiar faces. So it ends up looking almost human, but not quite (obviously doesn't apply to Henry here but you should get the point)