My guess:
In America cartoons are mainly for children (cel-shading looks cartoony)
In Japan they have anime and anime has a wider target group? (Much anime made for children, but there are also a lot of anime produced for an older audience).
I think this might have something to do with it...
The thing about trying to look mature by prefering things labeled as mature is valid argument as well I think.
And: cel-shading >>>>>>>>>>>CGI :p