This is not relevant to "Western" culture. It is relevant to US culture and East Asian culture, esp. Korea.
Western includes Europe and South America, and these cultures are not as infantile.
I like that advertising mascots were mentioned, like the Geico lizard. I also think software tools like standard Adobe illustrator tend toward a cartoon infantile look. Probably as a side effect for the need to make things vector scalable. It tends toward a flat big shape paradigm.
It also could be that companies like the idea of the customers as dependant upon the product, and infantilization fosters dependancy
Why? I have no idea.