Because it makes it cheaper to buy that car, which makes it more likely for someone to buy it, which increases sales, which allows Tesla to invest in improving

Because it makes it cheaper to buy that car, which makes it more likely for someone to buy it, which increases sales, which allows Tesla to invest in improving technology such as batteries and also to achieve economies of scale, which would allow prices to come down, which would lower the number of ice vehicles, which would lower the use of oil as an energy source, which would lower CO_2 emissions (and also pollution, international competition for resources, and the volatility of the mideast), which would lower the concentration of CO_2 in the atmosphere, which would allow more of the sun's irradiation heat to escape earth, which would slow the rise of global average temperature, which would lower the risk of widespread famine, death, war, impoverishment, migration, and mild unease that usually accompany major changes in the environment such as a countries' ability to grow food, or weather Austria needs a navy or not. But you kinda knew that already, right?