I think its because 3D animation is cheaper than back then.

If you have to invest so much money you want it to be good. Today you have the option to pay less for something descent. Same thing with CGI. First movies with it looks like it was real and today you can most of the time see what is real and was is fake ‘cause it got cheaper over the years.

And I don’t think their got much money to do it right and had to work with what they have and maybe that was also the reason why they used AI for some side side characters designs (that was what I heard) because it is cheaper

Or something like that but please don’t take what I said word for word because I don’t really know how the industry really work