it wasn't "some reason", it was 2D animators being unionized and 3D not being unionized. and the simple truth that capitalism kills art.
I remember when 2D faded out, the reason studios kept giving was "it's because 2D is a lot more expensive to produce". I was a child back then so I didn't think too much about it, assuming it was about the process itself, but as I grew up and learned more about art as an artist, and gained friends who were professional 3D artists themselves, I started to question it. Because 3D is very different from 2D, but it's definitely not easier or faster to make. Also, both European and Asian studios kept producing 2D animated movies
The answer was unions. The answer wasn't "this kind of art is cheaper because it's easier to make", it was "this kind of art is cheaper because these artists can't force us to pay them correctly"
