Apple VO2 Max Chart????

Can anyone explain why the VO2 chart that comes with Apple's health app, which links to the watch has a completely different set of numbers?

What really confuses me is how, when I have ramped up my activity level, my number continues to drop. Even though I know I am pushing it hard to trigger increases.

I understand to get an accurate VO2, a cardiopulmonary test must be done. Thus, Apple's health app is an estimated number. But it seems to be way off from the basic aerobic arithmetic calculation.