I disagree that it shows proportionality. Since we don't know where the zero would be with "thousands of cars", it could be way off the bottom of the chart, which means car numbers are relatively constant, even as stock price falls to a few percent of it's starting value.

The graph does show that both variables are decreasing, and that they both have a knee in the middle where the rate slows. But that's about all they clearly have in common.

An yes, scaling is of course necessary. It's translating that's the problem. I shouldn't have said scaling in my first post.