Don’t single Tesla out on this. No car manages to get its official mpg/EPA rating in real-world driving conditions. Some get closer than others and some manufacturers (eg Fiat) designed their motors in a way that maximises their performance on standardised tests. The gap between how ‘hard’ the car has to work to achieve the real world driving conditions vs test conditions plays a big part in the differential. Smaller motors with forced inductions are the worst offenders. Larger motors are more honest citizens.