It is weird, because it is not real, but the things its trying to observe are. Economics as a whole is also not as air tight as real science. Tho it seems to be trying. Just keep asking what is trying to be understood and why the figures presented represent the subject matter.

Think of how we measure the brightness, distance, and size of stars. We only have proxies that we can then calculate other values of interest. Economics is a lot of that with some human irrationality in the error bars as well.