Well I think it is simply a case of what wheels were designed for the car regarding looks. Which is of course subjective.
I put some 15" steel wheels with snow tires on my '05 New Beetle (that had 16" standard) and it looked a bit goofy. But the mechanicals didn't care, since it is the same as a 4th gen Golf/Jetta underneath, and all those used the same 15" wheels as standard.
What is the context of your question? What are you trying to accomplish? At this point, 16" wheels and tires are very common, and easily obtained.