Simpsons and Family Guy both started as traditional cel animation, 4:3 aspect ratio cartoons. Eventually they went digital paint and ink and to a wider 16:9 aspect ratio. I don’t think either show has looked as good as they did before the transition and I couldn’t figure out exactly why. BoJack Horseman, Rick and Morty and most anime series look great in 16:9 and hair thin outlines.
The difference is that neither show was really designed for a larger screen. They had to adapt as technology (TVs) improved. Essentially both shows got a lot more real-estate, but didn’t fill it with anything. Artistically the Simpsons residence looks more or less the same as it did when the show debuted in the late eighties. Peter Griffin still wears the same clothing as he did in 2001.
Copying and pasting from an old format to a new one rarely works out well without proper changes and design.