My car doesn’t have the model or engine size written on the back either, this is not exclusive to Tesla (although, depending on the make it might be an option to remove it when buying a car).
The manufacturer badge is usually enough, in my opinion. If you can’t identify the model on the spot, as long as you can identify the brand and want to learn about the specific model you saw, you’ll hit their website or dealership and identify it there. And with a brand like Tesla, that only has 5 fairly distinct models, it should be fairly easy to retroactively point out the model you saw - compared to a brand like BMW for example.