Telsa is in an enviable position of selling most of their cars before they're produced. In that position, you don't really need to advertise much. They also get a lot of PR to keep up brand awareness.

If Hyundai couldn't keep Genesis vehicles on the dealer lots, they'd advertise them less too. Having a dealer network means dealers that want manufacturer support in advertising to keep dealers happy, even if the new cars sell themselves, dealers need to get people in to sell used cars.