The wires in my Toyota are much thinner than the wires in any of my American cars were. I've had GM and Chryslers built from 1950 to 1995, and Toyotas from 2000 and 2005.
I'm not saying they are too thin, just thinner. Do you know why?
I see two poassible reasons.
1) Increased efforts to save money and help the environment, by using thinner and thus cheaper wire. Perhaps wires in American cars are thinnner now too??
2) Japan and the Japanese domestic auto industry after WWII was short of money and had to economize any way it could. Thinner, cheaper wires were one way, and now, even though they are making plenty money, they see no reason to change.
It matters only when I'm trying to splice wires, and I have to be more careful not to cut the wires while stripping the insulation. But the wires are so thin that there have been connections I don't try to make, because, where it's difficult to reach a wire, up under the dashboard, for example, that makes it even more likely I'll cut the wire and makes it harder to repair it.