Okay about Real world and Cartoon world stuff. Let me explain You see when we see the characters the Cartoon world You can see like Cell-Shading (or an Outline or a filter added) into the Characters, Sets, etc While the Real World (Well lets just say, Cell Shading not included) I understand your point about this thing and asking Why does the real world like the cartoon world but without Cell-Shading? Well If I have to guess They were planning on doing the whole Live Action thing for the Real World portions (kinda like the Garfield movie, the 2004 one but without the Garfield from that movie) But I guess the studio did not want to make another IRL Garfield movie in favor of doing Alvin and the Chipmunks (As in Rhythm and Hues Studios who did the Garfield stuff in the IRL Movies) So they have gotten the animation for the Cartoon world portions (along with the real world stuff) done mainly in Korea (Yes, It was done by Korean animators if you look at the credits of the movie) And if your wondering why the Real World characters look like they belong to the Cartoon world Well, My guess of that as well can be because I think Garfield Gets Real will become uncanny than the final product if they went with that Idea, LOL
Not only that, but the fact that there’s two more movies with the same animation. (it gave us one of the best Garfield shows of all time right next to Garfield and friends)