Not saying it's hard, only that it means more work
Don't know if you ever worked on animation, or ever had the curiosity to look it up how it works , so I'm gonna explain it.
Every character has one specific animator, and every animator must do all panels and moves of that character on the episode/movie til the deadline. Simple things like freckles, glasses, clothes etc means A LOT of more work at the big pile of papers you have to animate frame by frame.
Some key scenes requires so much that they have special teams to only work on that sequence. Something that, of course, can take months and inflate the budget.
For that reason a simple design is animation 101.
You can do a very fancy scene if you want it, but making ridiculously detailed characters only will make it twice as hard to animate it.
A big example is "The Thief and the Cobbler" that have ridiculously detailed sequences, but every character is pretty simple in concept.