Wax Ring question from a nonplumber

The Toto Onefit connections use a wax ring the the adapter joins the flange. I'm told that the wax ring seals out toxic sewer gases. However, it uses a rubber gasket where the toilet joins the adapter. If rubber is adequate to seal out sewer gases there, why can't rubber be used at the flange.

I have no earthly reason for asking this other than curiosity. Plus, I'm never sure a wax ring has adequately sealed since you aren't supposed to move the toilet once it is set, but you're supposed to level the toilet after it is set which can entail shimming, which to me involves moving. Wouldn't a more resilient rubber ring resolve that?

Signed,
Confused in the bathroom...

You can use rubber seals on the flange seal too.