I think they’re expensive and time-consuming in different ways.
2D animation you have to spend a lot of time actually drawing all the frames. Good-looking 2D animation is all done by hand. 3D animation is more like manipulating virtual puppets, and you can get a scene rough-cut a lot quicker, but it needs to bake for a long time in a rendering farm.
Obviously that’s simplifying it a lot, but my impression is for that reason 2D films take a lot more skill and man-hours, whereas 3D films take a lot of computing power.