Don't know much about CGI compositing but I think those CGI inserts in MMFR can be more complex than 100% CGI animation because the former has to blend in with the live action template. I could be wrong.
More hair & water would double the production cost??
Don't get me wrong, I think Zootopia may be Disney's new classic but
the costing is bizarre.
Edit: Warner & Illumination outsource their animations? Ok, that makes sense.