How Rfid Toll Tags Work (and What Happens When They Don't)

I once borrowed my parents Tesla, and drove it across a toll bridge. They said the RFID tag was in the glove box, and to take it out befoire crossing through the toll gate. I spent far too long driving somewhat destracted, while looking through the manual, trying to find the button to open the glove box, and eventually gave up. (It's in the settings menu, which is opened by taapping a car icon, in the lower left corner of the screen.)

They didn't have staffed gates, so it used a picture of the license plate, and my parents said it bills them the same, in case the tag isn't successfully read.

That had me wondering, why bother with the tag at all? License plate reading technology is far more reliable, and it reads the license plates of every vehicle that passes through the gate, so there's no purpose in the tag.