My guess is the uncanny valley[0] is still too big for "realistic" human characters. As for the goofy-looking chicken, it's convenient to make an animal goofy-looking for comic relief. (And in the case of Jiminy Cricket, I think Disney would rather draw, and people would rather look at, a humanoid with a weird head than an actual insect.)
[0] "the uncanny valley is the hypothesis that human replicas that appear almost, but not exactly, like real human beings elicit feelings of eeriness and revulsion among some observers" https://en.wikipedia.org/wiki/Uncanny_valley
[0] "the uncanny valley is the hypothesis that human replicas that appear almost, but not exactly, like real human beings elicit feelings of eeriness and revulsion among some observers" https://en.wikipedia.org/wiki/Uncanny_valley