The early Sierra style was born in programmer art and was pretty schematic, not much "style" at all. Green grass, blue water, fixed perspectives, rectangles and character templates. When they hired more trained artists, and when digital art had developed to allow it, a lot of games did go cartoony, yeah.
If you're making a animation that's the first thing you think of I suppose, but I would imagine the deciding factor was the comedy theme of most of these games. KQ didn't go cartoony until very late, right? But for Larry, MI, Space Quest, DOTT, S&M it's the obvious choice. The switch to cartoony style was long before high res came along. MI2 was cartoony! Look at most of the character and set designs, they are low res cartoons, that's all.
If you're making a animation that's the first thing you think of I suppose, but I would imagine the deciding factor was the comedy theme of most of these games. KQ didn't go cartoony until very late, right? But for Larry, MI, Space Quest, DOTT, S&M it's the obvious choice. The switch to cartoony style was long before high res came along. MI2 was cartoony! Look at most of the character and set designs, they are low res cartoons, that's all.