Internal combustion engines are very picky about how fast they spin, since they get their power from burning fuel the rate at which fuel enters the cylinders to burn correlates strongly to the power they have available. And since each cycle of a cylinder burns about the same amount of fuel the faster the engine spins the more power it generates.

This is why internal combustion engine vehicles have gearboxes (transmission in the US?) to ensure that you can spin the engine fast even while the wheels are slow) or stopped) so you have enough power to start the car.

Electric motors by contrast generate power through the strength of their electromagnetic fields, which is just how much current gets pushed through the electromagnets. How fast the motor spins just changes how fast the electronics have to "move" the generated field without changing the strength, so you get similar power even at slow speeds.

So electric motors have enough torque at low speed that you can start your car without needing a gearbox.

Note: this post is a gross simplification and probably mis-uses some terminology but it should give a general understanding of why the transmissions are different.

Okay pretend they are trains without tracks